放置一个按钮，在.cs 中实质按钮事件  


  protected void Button2_Click(object sender, EventArgs e)
    {
        System.Web.Security.FormsAuthentication.SignOut();
        //Response.Write("<script>window.opener=null;window.close();</script>");//注销并关闭窗口
        Response.Write("<script language=javascript>window.location.href='index.aspx';</script>");注销并返回
    }

Session.Abandon();
 Session.Clear();
 Response.Redirect("Default.aspx");