The traditional motor-driven servo proportional directional valve has the shortcomings of complex structure and poor dynamic characteristics.A large flow proportional directional valve driven by servo motor was designed,and constant differential pressure reducing valve was used to compensate pressure.The DC motor was used as the power component,and the valve core shaft was connected through the lead-screw nut mechanism to control the position of the main valve core.Double closed-loop control system was designed to improve the control accuracy of the valve core.The mathematical model of proportional directional valve was established based on the principle of dynamics.The steady-state and dynamic performance of proportional directional valve was theoretically analyzed.Furthermore,utilizing MATLAB/Simulink,the simulation model of proportional directional valve control system was established,and the steady-state and transient characteristics were simulated.The results show that the step response speed of the proportional directional valve reaches 36 ms.It is verified that the proposed proportional directional valve has good response speed and stability;through transient characteristic simulation,the curve of valve port flow of proportional directional valve changing with motor angle is obtained,and the control functions of motor angle and valve port flow characteristics are derived.It is verified that the constant differential pressure reducing valve can be used to compensate the pressure when the load changes,and the control accuracy of proportional directional valve can reach 98%.