弄了一个晚上,经过一个大牛的指点,10分钟搞定

procedure TMainForm.WebBrowser2DocumentComplete(Sender: TObject;
  const pDisp: IDispatch; var URL: OleVariant);
var
  oFrames:OleVariant;
begin
  oFrames := WebBrowser2.OleObject.document.forms;
  if oframes.length <> 0 then
  begin
  oFrames.item(0).submit;
  end;
end;