The authors present the pulsating parameter method in the frequency domain using two parameters of the pulsating model of an axial piston pump as major monitoring parameters to diagnose the fault of the pump. In order to apply the theory of transmission in a hydraulic pipeline to identify the model, a whole set of algorithms is also developed. Compared with existing methods, this method is much easier and cheaper to apply to hydraulic systems, less affected by the conditions of the environment, less sensitive to the errors in signal detection and data processing, and more sensitive to the faults of the pump.<<ETX>>