var my_fmt:TextFormat = new TextFormat();
my_fmt.font = "my font";//\\'my font\\'为库中字体元件的链接标识符
this.createTextField("my_txt",this.getNextHighestDepth(), 10, 10, 100, 22);
my_txt.border = true;
my_txt.embedFonts = true;//使用嵌入字体轮廓呈现文本字段
my_txt.text = "Hello World";
my_txt.setTextFormat(my_fmt);
my_txt._alpha = 20;

function setAlpha(obj, alpha) {
  var rgb = "0x"+(255*(100-alpha)/100).toString(16);
  rgb = rgb << 16 | rgb << 8 | rgb;
  obj.backgroundColor |= rgb;
  obj.borderColor |= rgb;
  obj.textColor |= rgb;
}

function setAlpha(obj, alpha) {
  var tmp_mc_name:String = obj._name+"_alphamask_mc";
  var tmp_mc:MovieClip = eval(tmp_mc_name);
  if (!tmp_mc) {
     tmp_mc = this.createEmptyMovieClip(tmp_mc_name,this.getNextHighestDepth());
     tmp_mc.beginFill(0xFFFFFF);
     tmp_mc.moveTo(0, 0);
     tmp_mc.lineTo(20, 0);
     tmp_mc.lineTo(20, 10);
     tmp_mc.lineTo(0, 10);
     tmp_mc.lineTo(0, 0);
     tmp_mc.endFill();
  }
  tmp_mc._x = obj._x;
  tmp_mc._y = obj._y;
  tmp_mc._width = (obj.border) ? obj._width+1 : obj._width;
  tmp_mc._height = (obj.border) ? obj._height+1 : obj._height;
  tmp_mc._alpha = 100-alpha;
}

this.createTextField("my_txt", this.getNextHighestDepth(), 10, 10, 100, 22);
my_txt.text = "Hello World";
setAlpha(my_txt,50);//设置my_txt文本透明度为50%