In order to realize the simulated loading of the hydraulic system, the loading experiment with the proportional relief valve as the loading element was designed, and the pressure closed-loop PID control of the system was realized.The measured value of the pressure sensor was compared with the set pressure value, and the difference was used as a control signal to adjust the valve port area of the proportional relief valve, so as to correct and adjust the actual pressure in real time to reach the set value.The experiments results show that the pressure loading closed-loop control system has strong resistance to flow disturbance.The closed-loop control system can eliminate the error between the pressure setting value and the actual value when there are flow step and slope interference signals. The closed-loop control system can make the actual pressure value maintaine with the set value and fluctuate slightly when there is a sinusoidal interference signal.