Compared with the traditional key to open the door and start the car, the keyless Passive Entry and Passive Start (PEPS) system realizes the complex bi-directional identity authentication between the car and the key through the communication between low frequency and radio frequency. In order to guarantee two-way identity authentication, this paper introduces the security authentication method of PEPS system based on UDS protocol in detail. Through the diagnostic learning function of UDS protocol, the authentication protection mechanism of remote keys and BCM, EMS, and ESCL is realized, which ensures the safety of the keyless PEPS system and provides strong technical support for its rapid development.