The authenticated key agreement protocols are widely used mechanisms for users to negotiate session keys and authenticate each other. Until now, there are many authenticated key agreement protocols proposed. However, many of them suffer from various attacks such as guessing attack, replay attack, impersonate attack, etc. In this paper, we propose a simple password-based authenticated key agreement protocol to solve these problems. The proposed protocol not only provides forward and backward secrecy, but also can resist replay attack, modification attack, and password guessing attack. Moreover, the computation cost of the protocol is very low.