嗯，简单地覆盖Form.ShowWithout Activation还不够吗？
protected override bool ShowWithoutActivation
{
get { return true; }
}
如果您也不希望用户单击此通知窗口，则可以覆盖CreateParams:
protected override CreateParams CreateParams
{
get
{
CreateParams baseParams = base.CreateParams;
const int WS_EX_NOACTIVATE = 0x08000000;
const int WS_EX_TOOLWINDOW = 0x00000080;
baseParams.ExStyle |= ( int )( WS_EX_NOACTIVATE | WS_EX_TOOLWINDOW );
return baseParams;
}
}