有2个意思：

1）形容某人比你差远了，你比某人好的太多了，根本没法比较。如Don't worry about him, he's got nothing on you. You're so much better.

2）形容某人没有任何可以用来控诉/***你的证据如Detective Gilmore knows that you murdered your wife, but he has nothing on you.这两个都是口语用法，说话时候才用的，别写到毕业论文里。