您需要监听键盘事件而不是鼠标事件。您在那里所做的是侦听图像上的 MouseEvent.CLICK 事件,这不是它应该如何工作的。
我的建议是你应该在舞台上监听键盘事件,然后检查是否按下了删除键。
还要检查这个 
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/events/KeyboardEvent.html#includeExamplesSummary上的 adobe 文档
http://livedocs.adobe.com/flex/3/html/help.html?content=events_11.html
请参阅此示例
package {
    import flash.display.Sprite;
    import flash.display.DisplayObject;
    import flash.events.*;
    public class KeyboardEventExample extends Sprite {
        private var child:Sprite = new Sprite();
        private var bgColor:uint = 0x00CCFF;
        private var size:uint = 80;
        public function KeyboardEventExample() {
            child.graphics.beginFill(bgColor);
            child.graphics.drawRect(0, 0, size, size);
            child.graphics.endFill();
            addChild(child);
            child.addEventListener(MouseEvent.CLICK, clickHandler);
            child.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
            child.addEventListener(KeyboardEvent.KEY_UP, keyUpHandler);
        }
        private function clickHandler(event:MouseEvent):void {
            stage.focus = child;
        }
        private function keyDownHandler(event:KeyboardEvent):void {
            trace("keyDownHandler: " + event.keyCode);
            trace("ctrlKey: " + event.ctrlKey);
            trace("keyLocation: " + event.keyLocation);
            trace("shiftKey: " + event.shiftKey);
            trace("altKey: " + event.altKey);
        }
        private function keyUpHandler(event:KeyboardEvent):void {
            trace("keyUpHandler: " + event.keyCode);
        }
    }
}