diff --git a/DLPilot/release/DLPilot.exe b/DLPilot/release/DLPilot.exe
index df0ea12..af3ed88 100644
Binary files a/DLPilot/release/DLPilot.exe and b/DLPilot/release/DLPilot.exe differ
diff --git a/DLPilot/src/app_gui.py b/DLPilot/src/app_gui.py
index 49b8980..3bfa930 100644
--- a/DLPilot/src/app_gui.py
+++ b/DLPilot/src/app_gui.py
@@ -63,10 +63,30 @@ def _apply_dropdown_theme():
     ctk.ThemeManager.theme['DropdownMenu']['text_color'] = ('#1A1A1A', '#DADADA')
 
 
+def _ensure_single_instance():
+    """单实例锁(Windows 命名互斥体): 已有实例在运行时返回 False。
+
+    双击 exe 开多个实例时, 只有先启动的能连串口, 后续实例连接报"拒绝访问",
+    且用户往往只看到后开的窗口 —— 表现为"连不上/断不开"。互斥体句柄随
+    进程存活, 进程退出自动释放。"""
+    ERROR_ALREADY_EXISTS = 183
+    ctypes.windll.kernel32.CreateMutexW(None, False, 'hulk.DLPilot.single')
+    return ctypes.windll.kernel32.GetLastError() != ERROR_ALREADY_EXISTS
+
+
 def run_gui(auto_close=0):
     """入口: 配置外观并启动主窗口"""
     ctk.set_appearance_mode('System')
     _apply_dropdown_theme()
+    if not _ensure_single_instance():
+        from tkinter import messagebox
+        import tkinter as tk
+        r = tk.Tk()
+        r.withdraw()
+        messagebox.showinfo('DLPilot 已在运行',
+                            '检测到另一个 DLPilot 实例正在运行。\n'
+                            '请使用已打开的窗口(串口同时只能被一个实例占用)。')
+        return
     App(auto_close).mainloop()
 
 
diff --git a/DLPilot/src/dlpc_rs485.py b/DLPilot/src/dlpc_rs485.py
index 72fe4d1..437e38f 100644
--- a/DLPilot/src/dlpc_rs485.py
+++ b/DLPilot/src/dlpc_rs485.py
@@ -301,7 +301,11 @@ class DLPC485:
                         self.ser = None
                         with self._lock:
                             self._target = None
-                        self.on_status(f'连接失败: {e}')
+                        et = str(e)
+                        if 'PermissionError' in repr(e) or '拒绝访问' in et \
+                                or 'Access is denied' in et:
+                            et += '（串口被占用: 检查串口助手/另一个本工具实例）'
+                        self.on_status(f'连接失败: {et}')
             if self.ser is not None:
                 try:
                     item = None