Abstract: In this paper we try to creat a method to diagnose and recognize the fault in a hydraulic system in accordance with different technical requirements and features of the system.The method is implemented by means of extracting fault information from pressure ripple,utilizing the autoregressive model parameters as the fault feature,and then using pattern recognition to classify what a fault pattern is existing.We have completed experimental study on the fault diagnosis of a pump system.The principle of this method is correct and the method is quite practical.