public class MyForm : Form

{

    protected override CreateParams CreateParams

    {

        get

        {

            const int WS_EX_APPWINDOW = 0x40000;

            const int WS_EX_TOOLWINDOW = 0x80;

            CreateParams cp = base.CreateParams;

            cp.ExStyle &= (~WS_EX_APPWINDOW);    // 不显示在TaskBar

            cp.ExStyle |= WS_EX_TOOLWINDOW;      // 不显示在Alt-Tab

            return cp;

        }

    }

}