var yubaostring = createTextField("txt", 0, 0, 0, Stage.width, 0);
yubaostring.autoSize = yubaostring.html=yubaostring.wordWrap=true;
yubaostring.selectable = false;
yubaostring._y = 2;
yubaostring._x = 0;
var countTime = 120;
var interval = setInterval(function () {
countTime--;
var minutes = Math.floor(countTime/60);
var seconds = countTime%60;
tty = "您试听时间剩余："+(((minutes<10) ? "0" : "")+minutes+":"+((seconds<10) ? "0" : "")+seconds);
yubaostring.htmlText = "<font face='微软雅黑' size='15' color='#FF0000'>"+tty+"</font>";
if (countTime == 0) {
clearInterval(interval);
//这里是你要执行
}
}, 1000);