DropDownList ddlprocess = (DropDownList)sender;
          DataListItem dl = (DataListItem)ddlprocess.Parent;
          HtmlGenericControl txttenorid = (HtmlGenericControl)dl.FindControl("tenorid");
          //Label txttenorid = (Label)dl.FindControl("tenorid");
          tenorid = txttenorid.InnerText.Trim();

終於搞定，不用那麼麻煩新增LABEL的，用一個隱藏的LABEL儲存ID也行的