Abstract: Kad network has become a main kind of file-sharing Peer-to-Peer(P2P) network,leading to the increasing demand of censoring it.In order to accurately determine the censoring object,the problem of optimal peer identification will be put forward.This paper tries to solve this problem.Kad network peer information crawler is designed and implemented to crawl peer information of multiple candidate identifications' relationship in real Kad network.Experimental results show that userID is the optimal peer identification.