------------------------------------------------
   $com_select = new  XoopsFormSelect('公司名稱', "com",'');
   $com_select->setExtra('onChange="change_com(this.value)"'); #指定改變值時執行的函數
   $com_select->addOption(0, "國泰人壽");
   $com_select->addOption(1, "富邦人壽");
   
   $dis_select = new  XoopsFormSelect('區部名稱', "dis",'');
   $dis_select->setExtra('onchange="this.form.submit();"');
   $dis_select->addOption(0, "國泰人壽南區1");
   $dis_select->addOption(1, "國泰人壽南區2");
   
   
    
    $form->addElement(new XoopsFormLabel("

自訂欄位

", 
      "
      //這裡用放script程式碼(前置)
      "), false);
      
    $form->addElement($com_select, true);
    
    $form->addElement($dis_select, true);
    
    $form->insertBreak("
    //這裡用放script程式碼(後置)
    

","ugm");
    # ----------------        結束表單程式 ------------------------------------
    $form->addElement(new XoopsFormHidden('uid', $user->getVar('uid') ));
    $form->addElement(new XoopsFormButton('', 'submit', _US_SAVECHANGES, 'submit'));
    #表單結束
   
    return $form; 
    
------------------------------------------------
ajax.php
------------------------------------------------
include 'admin_header.php';
$op=(empty($_REQUEST['op']))?"main":$_REQUEST['op'];
$com=(empty($_REQUEST['com']))?"":intval($_REQUEST['com']);

switch($op){
  //改變「menu_sn」, 更改類別排序
 case "ch_com":
    
    //$main=get_menu_prod_count($menu_sn,$prod_sort);
  
    #回傳排序及類別總數
    echo json_encode(array("op1"=>$op,"com1"=>$com));
    //echo "12345";
 break;
  
  //預設動作
  default:
  $main="";
  break;
}

ref:

http://blog.webugm.com/2012/11/20121121.html