package  {

    import flash.display.MovieClip;

    public class Main extends MovieClip {

        public function Main() {

            this.addChild(new Test());

        }

    }

}

package  {

    import flash.events.Event;

    import flash.display.Sprite;

    public class Test extends Sprite {

        public function Test() {

            this.addEventListener(Event.ADDED_TO_STAGE,init);

        }

        private function init(e:Event):void

        {

            //方法一

            this.parent["mc"].y = 120;

            //方法二

            //Main(parent).mc.y = 120;

            //方法三

            //Object(root).mc.y = 120;

        }

    }

}