>> CODE
var XmlReader = function(){
 this.GetHttpRequest = function(){
  if (window.XMLHttpRequest)  // Gecko
   return new XMLHttpRequest();
  else if (window.ActiveXObject) // IE
   return new ActiveXObject("MsXml2.XmlHttp") ;
 }
 this.LoadUrl = function(urlToCall, asyncFunctionPointer){
  var oXmlReader = this;
  var oXmlHttp = this.GetHttpRequest(); 
  oXmlHttp.open("GET", urlToCall, false); 
  oXmlHttp.send(null) ;
  if (oXmlHttp.status == 200)  this.DOMDocument = oXmlHttp.responseXML ;
  else alert("XML request error: " + oXmlHttp.statusText + " (" + oXmlHttp.status + ")") ; 
 }
 this.SelectNodes = function(xpath){
  if (document.all)  // IE
   return this.DOMDocument.selectNodes(xpath) ;
  else{     // Gecko
   var aNodeArray = new Array();
   var xPathResult = this.DOMDocument.evaluate(xpath, this.DOMDocument, this.DOMDocument.createNSResolver(this.DOMDocument.documentElement), XPathResult.ORDERED_NODE_ITERATOR_TYPE, null) ;
   if (xPathResult){
    var oNode = xPathResult.iterateNext() ;
    while(oNode){
     aNodeArray[aNodeArray.length] = oNode ;
     oNode = xPathResult.iterateNext();
    }
   }
   return aNodeArray ;
  }
 }
}

function show(field,pid,selid){
 var node = xmldoc.SelectNodes("//root/node[@pid="+pid+"]");
 field.innerHTML = null; //清除原来的option
 for(var i=0;i<node.length;++i) //增加省份名称到下拉列表
 {
  var oOption   = document.createElement('OPTION');
  oOption.text  = node[i].childNodes[0].nodeValue;
  oOption.value = node[i].getAttribute("id");
  if(oOption.value==selid) oOption.selected="selected";
  field.options.add(oOption);
 }
}

xml文档:

>> CODE
<?xml version="1.0" encoding="gb2312"?>
<root name="data_city" describe="省市联动">
  <node id="1" pid="0">江西</node>
  <node id="2" pid="1">九江</node>
  <node id="3" pid="1">南昌</node>
  <node id="4" pid="1">庐山</node>
  <node id="5" pid="1">景德镇</node>
 
  <node id="6" pid="0">北京</node>
  <node id="7" pid="6">北京西</node>
  <node id="8" pid="6">居庸关</node>
  <node id="9" pid="6">清华园</node>
  <node id="10" pid="6">周口店</node>

  <node id="11" pid="0">福建</node>
  <node id="12" pid="11">福州</node>
  <node id="13" pid="11">厦门</node>
  <node id="14" pid="11">漳州</node>

  <node id="15" pid="0">甘肃</node>
  <node id="16" pid="15">兰州</node>
  <node id="17" pid="15">洛门</node>
  <node id="18" pid="15">嘉峪关</node>

  <node id="19" pid="0">广东</node>
  <node id="20" pid="19">广州</node>
  <node id="21" pid="19">深圳</node>
  <node id="22" pid="19">东莞</node>
  <node id="23" pid="19">中山</node>