在程序的main函数中加入以下代码 bool createdNew; System.Threading.Mutex instance = new System.Threading.Mutex(true, "MutexName", out createdNew); if (createdNew) { Application.Run(new LoginForm()); instance.ReleaseMutex(); } else { Application.Exit(); } 还可以写成以下形式，一个窗体只能启动一次 Form1 a = new Form1(); bool createdNew; System.Threading.Mutex instance = new System.Threading.Mutex(true, "MutexName", out createdNew); if (createdNew) { a.ShowDialog(); instance.ReleaseMutex(); } else { a.Close(); }