const int WM_SYSCOMMAND = 0x0112; 
const int SC_CLOSE = 0xF060;  
 

protected override void WndProc(ref Message msg)
{ 
      
         if (msg.Msg == WM_SYSCOMMAND && ((int)msg.WParam == SC_CLOSE)) 
         { 
                 // 点击winform右上关闭按钮 
                return;
         } 
         base.WndProc(ref msg); 
}