Aiming at the problem that the temperature rise of the existing hydraulic loading system of the durability testing machine is too high and the micro internal leakage detection is not accurate enough,the hydraulic loading system of the rotary joint durability testing machine was designed,the function of pressure retaining and unloading was added,and the structure of the high pressure circuit supercharger was designed in detail.The thermal hydraulic simulation model of the complete hydraulic loading system was established by AMESim software,in the absence of a ready-made model,the simulation model of the rotary joint and the supercharger was constructed,and the system temperature rise simulation was completed.The changes of oil temperature under different working modes of the system were compared.The results show that the system oil temperature with unloading operation is 5 ℃ lower than that without unloading operation,which provides a reference for the design of hydraulic loading system and the prediction of system temperature rise.