清空页面上<input type="text" id="inputtext" runat="server

 private void ClearText()
    {
        foreach (System.Web.UI.Control control in Controls)
        {
            for (int i = 0; i < control.Controls.Count; i++)
            {
                if (control.Controls[i] is System.Web.UI.HtmlControls.HtmlInputControl)
                {
                    System.Web.UI.HtmlControls.HtmlInputControl tb =  (System.Web.UI.HtmlControls.HtmlInputControl)control.Controls[i];
                    tb.Value = "";
                }
            }
        }
    }