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();

}