Second, chooce a good time, take your child back to china without tell her, I think once you departure from the US costom, you wil be saftey even your wife find it at that time and call police.
However, Have you thought about your child's feeling? He would lose his Mom, how pain would it be for him? If he is not happy in rest his life, as his dad, would be happy? Better not to chooce this way!
It's difficult for you now, I understand, but don't give up, man, you're a man, other people can survive in USA, why can't you? Believe it, this tough time will pass soon compare to your whole life.
You may also collect the evidence that she has fault to break the marriage as well as the child's family, then the judge probably reward the custody of the child to you, so why flee away?
If you want to talk some more detail, I'd like to help you if you want.