Biometric authentication system has been widely used today, including fingerprint and face recognition systems. As for non-spot user authentication, compared with other biometric traits, speech has some advantages, such as high acceptability, low demand on quipments, flexible access anywhere and anytime, low computation complexity and suitability for remote authentication, which promotes the applications of speech based authentication system. However, playback becomes a general risk because of its easy carring out without any training, and the availability of cheap high quality audio recorder and speaker. This paper gives a through review to the methods for playback detection. It shows that the research is at the start point, but the demands are increasing.