With the fast development of the Mobile Internet , How to construct secure key agreement protocol is one of the most challenging in the unsafe mobile communications environment. In 2012, Gao Haiying proposed an efficient Identity Based authenticated key agreement protocol , which is proved to be secure in the standard model. Gao’s protocol was analysed and showed that it didn't provide PKG-forward secrecy in key escrowless mode. To solve this problem, a secure protocol was proposed. It also provided known-key security and forward secrecy resists key-compromise impersonation and unknown key share attacks. Results show that the protocol provides PKG-forward secrecy in escrowless mode .