The invention discloses a terminal, an identity authentication method, an authentication method for an authentication center and the terminal and an authentication system. The identity authentication method comprise the steps of randomly displaying a text; collecting an audio/video formed by reading the text, wherein the text is read by a user; extracting feature data in the audio/video; and judging whether the feature data matches the feature data in a database or not, if the feature data matches the feature data in the database, performing identity authentication, otherwise not performing the identity authentication. According to the terminal, the methods and the system, the text content displayed on the terminal is replaced continuously, so the audios/videos formed by reading the texts are different, wherein the texts are read by the user, the user can be authenticated according to the changed mouth shape feature data, and an illegal user is prevented from counterfeiting the same audio/video to simulate identity authentication. Compared with a mode of authenticating an identity through utilization of a cipher, the method has the advantages that the cipher does not need to be set, the defect that the security is low due to the fact that the cipher is liable to lose and steal is avoided, the authentication is assisted without configuring an extra device, only field authentication is carried out, and the authentication security is improved.