<script type="text/javascript" src="jquery/jquery-1.9.1.min.js"></script><script type="text/javascript">$(document).ready(function(){$.ajax({type:"get",dataType:"text",url:"GetItemAction?itemlevel=1", success:function(data){ // 由JSON字符串轉換為JSON對象  var objJSON=eval("("+data+")"); var len=objJSON.itemInfo.length;  var objSelect=document.getElementById("firstlevel"); for(var i=0;i<len;i++){ var op=new Option(objJSON.itemInfo[i].itemname,objJSON.itemInfo[i].itemcode); objSelect.add(op); }  },error: function (XMLHttpRequest, textStatus, errorThrown) {    alert(errorThrown);   }});});//顯示二級分類function firstlevel_Click(){var objfirst=document.getElementById("firstlevel");var index=objfirst.selectedIndex; //選中索引 var itemcode=objfirst.options[index].value; //選中值if(itemcode==0){alert("請選擇事件類別");return;}// 刪除二級分類保留第一個var objsecond=document.getElementById("secondlevel");for(var i=objsecond.options.length-1;i>0;i--){objsecond.options.remove(i);}// 刪除三級分類保留第一個var objthird=document.getElementById("thirdlevel");for(var i=objthird.options.length-1;i>0;i--){objthird.options.remove(i);}$.ajax({type:"get",dataType:"text",url:"GetItemAction?itemlevel=2&itemcode="+itemcode, success:function(data){ // 由JSON字符串轉換為JSON對象  var objJSON=eval("("+data+")"); var len=objJSON.itemInfo.length; var objSelect=document.getElementById("secondlevel"); for(var i=0;i<len;i++){ var op=new Option(objJSON.itemInfo[i].itemname,objJSON.itemInfo[i].itemcode); objSelect.add(op); }  },error: function (XMLHttpRequest, textStatus, errorThrown) {    alert(errorThrown);   }});}//顯示三級分類function secondlevel_Click(){var objsecond=document.getElementById("secondlevel");var index=objsecond.selectedIndex; //選中索引 var itemcode=objsecond.options[index].value; //選中值if(itemcode==0){alert("請選擇事件類別");return;}// 刪除三級分類保留第一個var objthird=document.getElementById("thirdlevel");for(var i=objthird.options.length-1;i>0;i--){objthird.options.remove(i);}$.ajax({type:"get",dataType:"text",url:"GetItemAction?itemlevel=3&itemcode="+itemcode, success:function(data){ // 由JSON字符串轉換為JSON對象  var objJSON=eval("("+data+")"); var len=objJSON.itemInfo.length; var objSelect=document.getElementById("thirdlevel"); for(var i=0;i<len;i++){ var op=new Option(objJSON.itemInfo[i].itemname,objJSON.itemInfo[i].itemcode); objSelect.add(op); }  },error: function (XMLHttpRequest, textStatus, errorThrown) {    alert(errorThrown);   }});}

<table class="table-exposure"> <tr> <td height="40"> <select id="firstlevel" onchange="firstlevel_Click()" style="width:99%;font-size:1em;"> <option value="0">請選擇事件大類</option> </select>      </td> </tr> <tr> <td height="40"> <select id="secondlevel" onchange="secondlevel_Click()" style="width:99%;font-size:1em;"> <option value="0">請選擇事件小類</option> </select> </td> </tr> <tr> <td height="40"> <select id="thirdlevel" style="width:99%;font-size:1em;"> <option value="0">請選擇事件類別</option> </select> </td> </tr> </table>