private void FrmMain_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Alt && e.Shift && e.Control && e.KeyCode == Keys.S)
    {
 MessageBox.Show("我按了Control +Shift +Alt +S");
    }
}

public class AppHotKey
{
        [DllImport("kernel32.dll")]
        public static extern uint GetLastError();
        //如果函數執(zhí)行成功，返回值不為0。
        //如果函數執(zhí)行失敗，返回值為0。要得到擴展錯誤信息，調用GetLastError。
        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool RegisterHotKey(
            IntPtr hWnd,                //要定義熱鍵的窗口的句柄
            int id,                     //定義熱鍵ID（不能與其它ID重復）          
            KeyModifiers fsModifiers,   //標識熱鍵是否在按Alt、Ctrl、Shift、Windows等鍵時才會生效
            Keys vk                     //定義熱鍵的內容
            );

        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool UnregisterHotKey(
            IntPtr hWnd,                //要取消熱鍵的窗口的句柄
            int id                      //要取消熱鍵的ID
            );

        //定義了輔助鍵的名稱（將數字轉變?yōu)樽址员阌谟洃?，也可去除此枚舉而直接使用數值）
        [Flags()]
        public enum KeyModifiers
        {
            None = 0,
            Alt = 1,
            Ctrl = 2,
            Shift = 4,
            WindowsKey = 8
        }
        /// <summary>
        /// 注冊熱鍵
        /// </summary>
        /// <param name="hwnd">窗口句柄</param>
        /// <param name="hotKey_id">熱鍵ID</param>
        /// <param name="keyModifiers">組合鍵</param>
        /// <param name="key">熱鍵</param>
        public static void RegKey(IntPtr hwnd, int hotKey_id, KeyModifiers keyModifiers, Keys key)
        {
            try
            {
                if (!RegisterHotKey(hwnd, hotKey_id, keyModifiers, key))
                {
                    if (Marshal.GetLastWin32Error() == 1409) { MessageBox.Show("熱鍵被占用 ！"); }
                    else
                    {
                        MessageBox.Show("注冊熱鍵失??！");
                    }
                }
            }
            catch (Exception) { }
        }
        /// <summary>
        /// 注銷熱鍵
        /// </summary>
        /// <param name="hwnd">窗口句柄</param>
        /// <param name="hotKey_id">熱鍵ID</param>
        public static void UnRegKey(IntPtr hwnd, int hotKey_id)
        {
            //注銷Id號為hotKey_id的熱鍵設定
            UnregisterHotKey(hwnd, hotKey_id);
        }
}

private const int WM_HOTKEY = 0x312; //窗口消息-熱鍵
private const int WM_CREATE = 0x1; //窗口消息-創(chuàng)建
private const int WM_DESTROY = 0x2; //窗口消息-銷毀
private const int Space = 0x3572; //熱鍵ID
protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    switch (m.Msg)
    {
 case WM_HOTKEY: //窗口消息-熱鍵ID
     switch (m.WParam.ToInt32())
     {
  case Space: //熱鍵ID
      MessageBox.Show("我按了Control +Shift +Alt +S");
      break;
  default:
      break;
     }
     break;
 case WM_CREATE: //窗口消息-創(chuàng)建
     AppHotKey.RegKey(Handle, Space, AppHotKey.KeyModifiers.Ctrl | AppHotKey.KeyModifiers.Shift | AppHotKey.KeyModifiers.Alt, Keys.S);
     break;
 case WM_DESTROY: //窗口消息-銷毀
     AppHotKey.UnRegKey(Handle, Space); //銷毀熱鍵
     break;
 default:
     break;
    }
}