Aiming at the difficulty of hydraulic cylinder fault diagnosis,a leakage fault diagnosis method of hydraulic cylinder based on distance recognition technology was proposed.The initial characteristic parameters such as time domain,frequency domain,wavelet packet energy features and AR model were extracted from the collected pressure signals;distance discrimination technology was used to select the characteristic parameters;the extracted sensitive fault features were input into SVM to detect leaks with different degrees.The results show that by using this method,the leakage of hydraulic actuator can be effectively detected.