<input type="submit" value="确定" class="dialogbtn"

 HtmlDocument doc = webBrowser1.Document;

             HtmlElementCollection coll = doc.GetElementsByTagName("input");

             foreach (HtmlElement item in coll)

             {

                 if (item.GetAttribute("value") == "确定")

                 {

                     item.InvokeMember("click");

                 }

             }