A mathematical model of proportional lowering valve was built to meet the requirement of electro-hydraulic lifter on high-power tractors. To improve the response characteristic and control accuracy of the hydraulic system, the model of the valve was established based on state space method. Then the influence on the dynamic characteristics of the valve was analyzed with respect to the parameter varieties of the components with the simulation and 4 steps Runge—Kutta method was adopted with Matlab/Simulink edited so as to obtain the optimum combination of the valve parameters. At last, the diameter of damping hole on pilot valve was 1.0mm, the diameter of damping hole on main valve was 1.2mm, the diameter of mainvalve larger face was 20mm, and the diameter of pilot valve was 8mm.