imgLogo.layer.masksToBounds= YES; //设置在layer之下的都盖住
imgLogo.layer.cornerRadius = imgLogo.bounds.size.width*0.5; //设置layer的圆角，是自身宽度的一半
imgLogo.layer.borderWidth=3.0; //圆角边框宽度
imgLogo.layer.borderColor = A_RGBA(173, 173, 173, 1).CGColor; //圆角颜色
原文：http://www.cnblogs.com/virgilko/p/4682044.html