diff --git a/README.md b/README.md
index ab2ef53..9b8115a 100644
--- a/README.md
+++ b/README.md
@@ -183,6 +183,28 @@ Native APIs only have simple set and get. tp.el provides three clear operation s
   ```
 - ✅ **Deep Merge**: `tp-add` recursively merges nested plist structures
 - ✅ **Smart Face Merging**: Symbol faces are automatically prepended to face lists, plist faces are deep merged
+- ✅ **Automatic Duplicate Property Merging in Single Call**: When the same property (e.g., `face`) is specified multiple times in a single `tp-set`/`tp-add`/`tp-reset` call, they are automatically merged
+
+```elisp
+;; Merge multiple faces in a single call
+(tp-set "emacs"
+        'face 'bold
+        'face '(:background "green")
+        'face '(:foreground "red"))
+;; Result: face is ((:background "green" :foreground "red") bold)
+
+;; Later values override earlier ones for the same sub-property
+(tp-set "emacs"
+        'face '(:foreground "red")
+        'face '(:foreground "yellow"))
+;; Result: foreground is "yellow"
+
+;; Use with tp-palette layer
+(tp-set "emacs"
+        'tp-palette 'info
+        'face '(:foreground "red"))
+;; Result: tp-palette's face is merged with (:foreground "red")
+```
 
 ### Innovative Property Layer System
 
@@ -471,6 +493,25 @@ LAYER-NAME can be a symbol representing a layer defined by `tp-define-layer` or
   :data ((my-color . "blue")))
 (tp-set " " 'my-style)
 ;; => #(" " 0 1 (tp-name my-style face (:foreground "blue") ...))
+
+;; Merge multiple faces in a single call (duplicate properties auto-merged)
+(tp-set "emacs"
+        'face 'bold
+        'face '(:background "green")
+        'face '(:foreground "red"))
+;; => Three faces merged into one: ((:background "green" :foreground "red") bold)
+
+;; Later values override earlier ones for the same sub-property
+(tp-set "emacs"
+        'face '(:foreground "red")
+        'face '(:foreground "yellow"))
+;; => face's :foreground is "yellow" (later overrides earlier)
+
+;; Use with tp-palette layer, merging extra face properties
+(tp-set "emacs"
+        'tp-palette 'info
+        'face '(:foreground "red"))
+;; => tp-palette's face is merged with (:foreground "red"), :foreground is overridden
 ```
 
 ---
diff --git a/README_CN.md b/README_CN.md
index ecfb0f6..c158ffe 100644
--- a/README_CN.md
+++ b/README_CN.md
@@ -182,6 +182,28 @@
   ```
 - ✅ **深度合并**：`tp-add` 递归合并嵌套的 plist 结构
 - ✅ **Face 智能合并**：符号 face 自动前置到 face 列表，plist face 深度合并
+- ✅ **单次设置中的重复属性自动合并**：在一次 `tp-set`/`tp-add`/`tp-reset` 调用中，如果同一属性（如 `face`）被指定多次，它们会自动合并
+
+```elisp
+;; 单次调用中合并多个 face
+(tp-set "emacs"
+        'face 'bold
+        'face '(:background "green")
+        'face '(:foreground "red"))
+;; 结果: face 是 ((:background "green" :foreground "red") bold)
+
+;; 同一子属性后面的覆盖前面的
+(tp-set "emacs"
+        'face '(:foreground "red")
+        'face '(:foreground "yellow"))
+;; 结果: foreground 是 "yellow"
+
+;; 与 tp-palette 层配合使用
+(tp-set "emacs"
+        'tp-palette 'info
+        'face '(:foreground "red"))
+;; 结果: tp-palette 的 face 与 (:foreground "red") 合并
+```
 
 ### 创新的属性层系统
 
@@ -462,6 +484,25 @@ LAYER-NAME 可以是通过 `tp-define-layer` 定义的层名称或通过 `tp-def
   :data '((my-color . "blue")))
 (tp-set " " 'my-style)
 ;; => #(" " 0 1 (tp-name my-style face (:foreground "blue") ...))
+
+;; 单次调用中合并多个 face（重复属性自动合并）
+(tp-set "emacs"
+        'face 'bold
+        'face '(:background "green")
+        'face '(:foreground "red"))
+;; => 三个 face 合并为一个: ((:background "green" :foreground "red") bold)
+
+;; 同一子属性后面的值覆盖前面的
+(tp-set "emacs"
+        'face '(:foreground "red")
+        'face '(:foreground "yellow"))
+;; => face 的 :foreground 是 "yellow"（后面的覆盖前面的）
+
+;; 与 tp-palette 层配合使用，合并额外的 face 属性
+(tp-set "emacs"
+        'tp-palette 'info
+        'face '(:foreground "red"))
+;; => tp-palette 的 face 与 (:foreground "red") 合并，:foreground 被覆盖
 ```
 
 ---
diff --git a/tp-tests.el b/tp-tests.el
index 39990b0..99707af 100644
--- a/tp-tests.el
+++ b/tp-tests.el
@@ -3702,5 +3702,163 @@ internally, and the final result should have face properties, not tp-palette."
       (should (null (get-text-property 0 'tp-test-level1 result)))
       (should (null (get-text-property 0 'tp-test-level2 result))))))
 
+;;; ============================================================
+;;; Duplicate Property Merging Tests
+;;; ============================================================
+
+(ert-deftest tp-test-merge-duplicate-face-symbols ()
+  "Test that multiple face symbols in one call are merged into a face list."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'face 'bold
+                          'face 'italic)))
+      ;; Should be a list with italic first (later takes precedence)
+      (let ((face-prop (get-text-property 0 'face result)))
+        (should (listp face-prop))
+        (should (memq 'bold face-prop))
+        (should (memq 'italic face-prop))
+        ;; italic should come before bold (later value takes precedence)
+        (should (< (cl-position 'italic face-prop)
+                   (cl-position 'bold face-prop)))))))
+
+(ert-deftest tp-test-merge-duplicate-face-plists ()
+  "Test that multiple face plists in one call are merged."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'face '(:background "green")
+                          'face '(:foreground "red"))))
+      (let ((face-prop (get-text-property 0 'face result)))
+        ;; Should be a merged plist
+        (should (plist-get face-prop :background))
+        (should (plist-get face-prop :foreground))
+        (should (equal (plist-get face-prop :background) "green"))
+        (should (equal (plist-get face-prop :foreground) "red"))))))
+
+(ert-deftest tp-test-merge-duplicate-face-later-overrides ()
+  "Test that later face plist values override earlier ones for same key."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'face '(:foreground "red")
+                          'face '(:foreground "yellow"))))
+      (let ((face-prop (get-text-property 0 'face result)))
+        ;; Later value should override
+        (should (equal (plist-get face-prop :foreground) "yellow"))))))
+
+(ert-deftest tp-test-merge-face-symbol-and-plist ()
+  "Test merging face symbol with face plist."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'face 'bold
+                          'face '(:background "green")
+                          'face '(:foreground "red"))))
+      (let ((face-prop (get-text-property 0 'face result)))
+        ;; Should be a list with plist and symbol
+        (should (listp face-prop))
+        ;; First element should be the merged plist (plists merge together)
+        (should (listp (car face-prop)))
+        (should (keywordp (caar face-prop)))
+        ;; Check the merged plist has both properties
+        (let ((merged-plist (car face-prop)))
+          (should (equal (plist-get merged-plist :background) "green"))
+          (should (equal (plist-get merged-plist :foreground) "red")))
+        ;; bold should be in the list
+        (should (memq 'bold face-prop))))))
+
+(ert-deftest tp-test-merge-other-props-later-overrides ()
+  "Test that non-face duplicate properties use later value."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'help-echo "first"
+                          'help-echo "second")))
+      (should (equal (get-text-property 0 'help-echo result) "second")))))
+
+(ert-deftest tp-test-merge-with-palette-layer ()
+  "Test merging face from tp-palette layer with extra face property."
+  (tp-test-with-temp-buffer
+    ;; Redefine tp-palette since tp-test-with-temp-buffer resets tp-layer-alist
+    (define-tp tp-palette (symbol)
+      (let ((palette (intern (concat "tp-palette-"
+                                     (symbol-name symbol)))))
+        `(face ( :foreground ,(tp-palette-fg-color palette)
+                 :background ,(tp-palette-bg-color palette)
+                 :box (:color ,(tp-palette-border-color palette))))))
+    (let ((result (tp-set "emacs"
+                          'tp-palette 'info
+                          'face '(:foreground "red"))))
+      (let ((face-prop (get-text-property 0 'face result)))
+        ;; The face from tp-palette should be merged with :foreground "red"
+        ;; With :foreground "red" overriding the palette's foreground
+        (should (equal (plist-get face-prop :foreground) "red"))
+        ;; Background from palette should still be present
+        (should (plist-get face-prop :background))
+        ;; Box from palette should still be present
+        (should (plist-get face-prop :box))))))
+
+(ert-deftest tp-test-merge-multiple-layers-with-face ()
+  "Test merging multiple layers that each contribute face properties."
+  (tp-test-with-temp-buffer
+    (define-tp tp-test-layer1 ()
+      '(face (:foreground "blue")))
+    (define-tp tp-test-layer2 ()
+      '(face (:background "yellow")))
+    (let ((result (tp-set "emacs"
+                          'tp-test-layer1 t
+                          'tp-test-layer2 t
+                          'face '(:weight bold))))
+      (let ((face-prop (get-text-property 0 'face result)))
+        ;; All face properties should be merged
+        (should (equal (plist-get face-prop :foreground) "blue"))
+        (should (equal (plist-get face-prop :background) "yellow"))
+        (should (equal (plist-get face-prop :weight) 'bold))))))
+
+(ert-deftest tp-test-merge-in-region-form ()
+  "Test duplicate property merging in region form."
+  (tp-test-with-temp-buffer
+    (insert "Hello World")
+    (tp-set 1 6 '(face bold face (:foreground "green")))
+    (let ((face-prop (tp-at 1 'face)))
+      ;; Should be a list with plist and symbol
+      (should (listp face-prop))
+      ;; Check properties
+      (should (or (memq 'bold face-prop)
+                  (eq face-prop 'bold))))))
+
+(ert-deftest tp-test-tp-add-merge-faces ()
+  "Test that tp-add also merges duplicate face properties."
+  (tp-test-with-temp-buffer
+    (insert "Hello World")
+    (tp-add 1 6 '(face bold face (:foreground "red")))
+    (let ((face-prop (tp-at 1 'face)))
+      ;; Should have both face values merged
+      (should (listp face-prop))
+      (should (memq 'bold face-prop))
+      ;; Check for the plist part with :foreground
+      (should (cl-some (lambda (f)
+                         (and (listp f)
+                              (keywordp (car f))
+                              (equal (plist-get f :foreground) "red")))
+                       face-prop)))))
+
+(ert-deftest tp-test-tp-reset-merge-faces ()
+  "Test that tp-reset also merges duplicate face properties."
+  (tp-test-with-temp-buffer
+    (insert "Hello World")
+    (tp-reset 1 6 '(face bold face (:foreground "red")))
+    (let ((face-prop (tp-at 1 'face)))
+      ;; Should have both face values merged
+      (should (listp face-prop))
+      (should (memq 'bold face-prop)))))
+
+(ert-deftest tp-test-merge-mouse-face ()
+  "Test that mouse-face properties are also merged."
+  (tp-test-with-temp-buffer
+    (let ((result (tp-set "emacs"
+                          'mouse-face 'highlight
+                          'mouse-face '(:background "blue"))))
+      (let ((mouse-face-prop (get-text-property 0 'mouse-face result)))
+        ;; Should be a list with plist and symbol
+        (should (listp mouse-face-prop))
+        (should (memq 'highlight mouse-face-prop))))))
+
 (provide 'tp-ert-tests)
 ;;; tp-ert-tests.el ends here
diff --git a/tp.el b/tp.el
index 6afc5c9..9e9fa5c 100644
--- a/tp.el
+++ b/tp.el
@@ -244,6 +244,106 @@ NEW values override BASE values."
                   (t val))))))
     result))
 
+(defun tp--merge-face-values (face1 face2)
+  "Merge two face values into one.
+FACE1 is the earlier value, FACE2 is the later value.
+For face plists (like (:foreground \"red\")), merge with later overriding.
+For symbol faces, create a list with FACE2 taking precedence.
+Returns the merged face value."
+  (cond
+   ;; No earlier face - just use later face
+   ((null face1) face2)
+   ;; No later face - just use earlier face
+   ((null face2) face1)
+   ;; Both are plists - merge with later overriding earlier
+   ((and (listp face1) (keywordp (car-safe face1))
+         (listp face2) (keywordp (car-safe face2)))
+    (tp--deep-merge-plist face1 face2))
+   ;; Later is a plist, earlier is a symbol or list of faces
+   ((and (listp face2) (keywordp (car-safe face2)))
+    (cond
+     ((symbolp face1)
+      (list face2 face1))
+     ((listp face1)
+      (cons face2 face1))
+     (t face2)))
+   ;; Earlier is a plist, later is a symbol
+   ((and (listp face1) (keywordp (car-safe face1))
+         (symbolp face2))
+    (list face2 face1))
+   ;; Later is a symbol - prepend to earlier
+   ((symbolp face2)
+    (cond
+     ((symbolp face1)
+      (if (eq face1 face2)
+          face2
+        (list face2 face1)))
+     ((listp face1)
+      (if (member face2 face1)
+          (cons face2 (remove face2 face1))  ; Move to front
+        (cons face2 face1)))
+     (t face2)))
+   ;; Later is a list of faces - prepend to earlier
+   ((listp face2)
+    (cond
+     ((symbolp face1)
+      (if (member face1 face2)
+          face2
+        (append face2 (list face1))))
+     ((listp face1)
+      (append face2
+              (cl-remove-if (lambda (f) (member f face2)) face1)))
+     (t face2)))
+   (t face2)))
+
+(defun tp--merge-duplicate-keys (plist)
+  "Merge duplicate keys in PLIST into a single key-value pair.
+For `face' and `font-lock-face' properties, values are merged so that
+later values take precedence over earlier ones for the same sub-properties.
+For other properties, later values override earlier ones.
+
+This function is designed for single-call property setting where multiple
+properties of the same type can be specified and should be merged.
+
+Example:
+  (tp--merge-duplicate-keys \\='(face bold face (:foreground \"red\")))
+  => (face ((:foreground \"red\") bold))
+
+  (tp--merge-duplicate-keys \\='(face (:background \"blue\") face (:foreground \"red\")))
+  => (face (:background \"blue\" :foreground \"red\"))
+
+  (tp--merge-duplicate-keys \\='(prop1 a prop2 b prop1 c))
+  => (prop1 c prop2 b)"
+  (let ((key-values (make-hash-table :test 'eq))
+        (key-order nil))
+    ;; Collect all values for each key in order
+    (cl-loop for (key val) on plist by #'cddr
+             do (progn
+                  (unless (gethash key key-values)
+                    (push key key-order))
+                  (puthash key
+                           (cons val (gethash key key-values))
+                           key-values)))
+    ;; Reverse key-order to get original order
+    (setq key-order (nreverse key-order))
+    ;; Build result plist by merging values for each key
+    (let ((result nil))
+      (dolist (key key-order)
+        (let ((values (nreverse (gethash key key-values))))  ; Reverse to get original order
+          (if (= (length values) 1)
+              ;; Single value - use as-is
+              (setq result (append result (list key (car values))))
+            ;; Multiple values - merge them
+            (let ((merged-val
+                   (cond
+                    ;; Face properties - use special face merging
+                    ((memq key '(face font-lock-face mouse-face))
+                     (cl-reduce #'tp--merge-face-values values))
+                    ;; Other properties - later overrides earlier
+                    (t (car (last values))))))
+              (setq result (append result (list key merged-val)))))))
+      result)))
+
 (defun tp--get-nested (value path)
   "Get nested value from VALUE following PATH (list of keys).
 Supports plists, alists, and list-of-keys extraction."
@@ -964,6 +1064,11 @@ Supports multiple calling conventions:
     ;; Unwrap double-wrapped properties
     (when (and (listp props) (listp (car-safe props)))
       (setq props (car props)))
+    ;; Merge duplicate keys in the plist (for single-call property setting)
+    ;; This must happen before tp--resolve-props to properly handle face merging
+    ;; Use (cddr props) for O(1) check instead of (> (length props) 2)
+    (when (and (listp props) (cddr props))
+      (setq props (tp--merge-duplicate-keys props)))
     ;; Resolve props: handles layer/group names and anonymous reactive plists
     (when props
       (setq props (or (tp--resolve-props props) props)))
@@ -2762,7 +2867,11 @@ Returns the expanded plist."
          (t
           (setq result (append result (list key val)))))
         (setq remaining (cddr remaining))))
-    result))
+    ;; Merge duplicate keys in the expanded result
+    ;; Use (cddr result) for O(1) check instead of (> (length result) 2)
+    (if (cddr result)
+        (tp--merge-duplicate-keys result)
+      result)))
 
 (defun tp--resolve-props (props)
   "Resolve PROPS to a property list with layer metadata.