话不多说，参考代码中的注释
var pice = 8;
//瓣数
var amp = 180;
//半径
x0 = 550/2;
//中心X坐标
y0 = 400/2;
//中心Y坐标
degree = 0;
//初始角
speed = 2;
//画线速度
colorF = 0xFF0000;
//线条颜色
_root.createEmptyMovieClip("flower", 1);
//创建MC
with (flower) {
   flower.moveTo(x0+amp, y0);
   //移动起始点
   flower.lineStyle(3, colorF, 100);
   //定义线条样式
}
flower.onEnterFrame = function() {
   //开始画线
   if (degree<=360) {
      for (i=1; i<=speed; i++) {
         radian = Math.PI/180*(degree);
         p = amp*Math.cos(pice/2*radian);
         x = x0+p*Math.cos(radian);
         y = y0+p*Math.sin(radian);
         this.lineTo(x, y);
         degree++;
      }
   }
};