Based on the nonlinear characteristics of hydraulic system of wearable rehabilitation training robot and the diversity of fault forms, in order to reflect the operational stability of hydraulic system of the wearable rehabilitation training robot,the fault mechanism of hydraulic drive system was analyzed,and the fault of nonlinear hydraulic system was studied. The fault signal of hydraulic drive system was simulated by AMESim ，ADAMS and MATLAB, then the corresponding fault response curves were compared with the normal response curve.After analyzing the results of simulation, the fault type of hydraulic system was determined and carried out to improve the diagnosis.The aim is to further improve the stability of rehabilitation training robot to drive system.