In order to solve the problem that the fault diagnosis of a rocket launcher hydraulic system was less and the fault knowledge was difficult to get, the rocket launcher hydraulic system was used as the research object,ADAMS and EASY5 software were used to build the virtual prototype model, the accuracy of the model was checked by comparing the simulation results and testing results. On the basis, the principle of hydraulic failure was analyzed, and the failure modes of hydraulic pump leakage, oil entrained air and filter clogging were completed by modifying the model parameters or equivalent modeling. The effects of different fault conditions on the performance of the system were calculated. The simulation results are in agreement with the theoretical analysis. The results show that fault knowledge and samples can be obtained through fault simulation, which can provide reference for hydraulic system fault diagnosis and have guiding significance for maintenance of the equipment.