It's the time

toShow="打字效果就自动出来了。"

var i:Number = 0;
onEnterFrame = function () {
  i += 1.2;
  txt.text = toShow.substr(0, i);
  //txt动态文本框的名字
  if (i > toShow.length)
  {
    delete this.onEnterFrame;
    i = 0;
  }
};