With the unceasing development of the mobile IPv6 technology, the users have put forward higher requirements for the security of the network. According to the proxy mobile IPv6 binding update process safety issues, this paper improves the return path process, basing on the Return Routability Procedure and the Asymmetric cryptographic technique. It proposes one kind of security mechanism based on the automatic key authentication. The paper analyses the security of the scheme, which can effectively prevent attackers from forging, tampering the messages, denying the mobile host being attacked by a series of problems, such as the denial of service.