Использование URLLoader
var ldr:URLLoader = new URLLoader();
var request:URLRequest = new URLRequest("file.xml");
ldr.addEventListener(Event.COMPLETE, onLoad);
ldr.load(request);
private function onLoad(e:Event):void
{
var ldr:URLLoader = URLLoader(e.target);
trace(ldr.data);//traces the string content of file
var myxml:XML = new XML(ldr.data);
trace(myxml.toXMLString());
}