//draw circle line for the preloader
var cos:Function=Math.cos;
var sin:Function=Math.sin;
var pi:Number=Math.PI;
var d_r:Number=pi/180;
var r_d:Number=180/pi;
var midPoint:Object={_x:0,_y:0};
var r:Number=11;

var pLoaded=Math.round(event.target.bytesLoaded*100/event.target.bytesTotal);

mcPreloader.graphics.clear();
mcPreloader.graphics.lineStyle(3);
mcPreloader.graphics.moveTo(11,0);

for (var z = 0; z<=pLoaded*3.6; z++) {
	mcPreloader.graphics.lineTo((cos(z*d_r)*r), (sin(z*d_r)*r));
}

Draw circle preloader

ActionScript 3