//假设html有表单 id="Form1"
HtmlElement htmlForm= webBrowser1.Document.GetElementById("Form1");
htmlForm.InvokeMember("submit"); //大小写忘记了自己试验和js 一样的看看 dhtml 帮助可以
            
//假设html有提交按钮id="Submit"
HtmlElement btn_Submit= this.webbrowser1.Document.GetElementById("Submit");   
btn_Submit.InvokeMember("click");