Hydraulic fluid compressibility is an important parameter for the modeling and analysis of hydraulic system,which has great influence on the dynamic response characteristics of hydraulic control system.The corresponding mathematical model was established by analyzing the electro-hydraulic proportional pressure regulating system,in which the oil compressibility was introduced.AMESim was used to build its simulation model.The simulation results show that hydraulic fluid compressibility has little effect on the static characteristics of electro-hydraulic proportional relief valve and electro-hydraulic proportional pressure regulating system;it has great influence on the dynamic characteristics of electro-hydraulic proportional relief valve and electro-hydraulic proportional pressure regulating system.The simulation results provide theoretical support for the design of electro-hydraulic proportional pressure regulating system.