public static void OpenPopUp(System.Web.UI.WebControls.WebControl opener,string PagePath,string windowName,int Top,int Left,int width,int height)
{
    string clientScript;
    string windowAttribs;
    windowAttribs = "left=" + Left.ToString() + "px," +
  "top=" + Top.ToString() + "px," +
  "width=" + width.ToString() + "px," + 
  "height=" + height.ToString() + "px," +
  "left=''''+((screen.width -" + width.ToString()+ ") / 2)+'''',";
  clientScript = "window.open(''''"+PagePath+ "'''',''''"+   
                                windowName + "'''',''''"+ windowAttribs + "'''');return false;";
    opener.Attributes.Add("onClick", clientScript);
}

private void Page_Load(object sender, System.EventArgs e)
{
    // 在此处放置用户代码以初始化页面
    if(!IsPostBack)
    {
 OpenPopUp(Button1,"http://www.google.com";);
 OpenPopUp(Button2,"http://www.google.com";,"",0,0,300,300);
    }
}