The three position fourway electromagnetic directional valve was taken as the research object, The motion mechanism of solenoid valve spool was analyzed, model was established by using multiphysics coupling mathematical model establishment method, and a mathematical models of dynamic response of solenoid valve spool work process was established. In AMESim software environment,solenoid valve model was established. Using the established model, the factors affecting the solenoid valve spool displacement was analyzed. By changing in the model of spring stiffness, a group of spool displacement curves was gotten.The result shows that when spring aging, spool displacement will increase in the same input, let the hydraulic system security risk. Finally, the modle is verified by experiment.