public function index(){
  $province = M('Tree')->where ( array('pid'=>1) )->select ();
  $this->assign('province',$province);
  $this->display();
}
public function getRegion(){
  $Region=M("Tree");
  $map['pid']=$_REQUEST["pid"];
  $map['type']=$_REQUEST["type"];
  $list=$Region->where($map)->select();
  echo json_encode($list);
}

<select name="province" id="province" onchange="loadRegion('province',2,'city','{:U('Index/getRegion')}');">
  <option value="0" selected>省份/直辖市</option><volist name="province" id="vo">
  <option value="{$vo.id}" >{$vo.name}</option></volist>
</select>
<select name="city" id="city" onchange="loadRegion('city',3,'town','{:U('Index/getRegion')}');">
 <option value="0">市/县</option>
</select>
<select name="town" id="town">
 <option value="0">镇/区</option>
</select>

function loadRegion(sel,type_id,selName,url){
  jQuery("#"+selName+" option").each(function(){
    jQuery(this).remove();
  });
  jQuery("<option value=0>请选择</option>").appendTo(jQuery("#"+selName));
  if(jQuery("#"+sel).val()==0){
    return;
  }
  jQuery.getJSON(url,{pid:jQuery("#"+sel).val(),type:type_id},
    function(data){
      if(data){
        jQuery.each(data,function(idx,item){
          jQuery("<option value="+item.id+">"+item.name+"</option>").appendTo(jQuery("#"+selName));
        });
      }else{
        jQuery("<option value='0'>请选择</option>").appendTo(jQuery("#"+selName));
      }
    }
  );
}

DROP TABLE IF EXISTS `tp_tree`;
CREATE TABLE `tp_tree` (
 `id` int(5) unsigned NOT NULL AUTO_INCREMENT,
 `pid` int(5) unsigned NOT NULL DEFAULT '0',
 `name` varchar(120) DEFAULT NULL,
 `type` tinyint(1) DEFAULT '2',
 PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3410 DEFAULT CHARSET=utf8;