In the hydraulic control system of the hydraulic automatic derailleur,the demand for the working pressure of the shift operation varies greatly under different working conditions,so a multi-stage main pressure valve is often used.During the working process,the change of the overflow volume will cause the constant pressure error of the main pressure valve,which will affect the performance of the system.In order to improve the constant pressure accuracy of the main pressure valve,a proportional main pressure control strategy for the multi-stage main pressure valve was proposed.The working principle of the multi-stage main pressure valve was introduced,the mathematical model of the multi-stage main pressure valve was deduced,and the dynamic simulation of the pressure regulating characteristics of the multi-stage main pressure valve was carried out in Simulink.Then,a method of connecting proportional pressure reducing valve in the feedback chamber was proposed.Through closed-loop control of the output pressure of the proportional pressure reducing valve,the pressure of the feedback chamber could be continuously changed within a range,thereby realizing the continuous change of the output pressure of the main pressure valve.Finally,a pressure closed-loop control strategy for the main pressure was proposed to improve the matching accuracy of the main pressure.The results show that the multi-stage main pressure valve can quickly realize the pressure setting under different working conditions,and the continuous control of the main pressure can be realized by the proportional pressure reducing valve,which improves the constant pressure accuracy of the system and the phenomenon of pressure dropping caused by the load flow burst is optimized.