protected void ClearTextBoxes(Control p1)
{
    foreach (Control ctrl in p1.Controls)
    {
        if(ctrl is TextBox)
        {
             TextBox t = ctrl as TextBox;

             if(t != null)
             {
                  t.Text = String.Empty;
             }
        }
        else
       {
           if (ctrl.Controls.Count > 0)
           {
               ClearTextBoxes(ctrl);
           }
        }
    }
}

然后在您的点击事件中调用它，如下所示：

ClearTextBoxes(Page);