var exist = new LoadVars();
exist.onLoad = function(success) {
if(!success) {
trace("文件不存在");
}
}
exist.load("文件名");

var exist = new LoadVars();
this.createEmptyMovieClip("item_mc", this.getNextHighestDepth());
item_mc.onEnterFrame=function(){
var total =this.target.getBytesTotal();
if(int(total)>101){
//這里沒有使用total==undefined判斷，因為發現不準，文件不存在時int(total)=101
delete item_mc.onEnterFrame;
trace("文件存在");
trace(int(total));//返回總字節
}
}
item_mc.target=exist;
exist.load("文件地址");