Abstract: In order to study the influence of the structural parameters of the jet pipe servo valve on the performance of the pilot stage, a pilot stage numerical model of the servo valve was established, and the numerical simulation results of the pilot stage flow field was verified by using the PIV technology. The effects of nozzle hole diameter, receiving hole diameter and distance between nozzle and receiver on the restoring pressure difference and its stability were analyzed by means of numerical method. The optimum matching range of structural parameters of the pilot stage under three different flow rates of servo valves was obtained. The results show that, when the diameter of the nozzle is 0.22~0.28 mm, the optimum range of the diameter ratio of the receiving hole to the nozzle hole diameter is 1.1~1.2, and the optimum range of the ratio of the distance between nozzle and receiver to the nozzle hole diameter is 0.6~0.8. The pilot stage structure parameters have a direct influence on the stability of the differential pressure of the receiving hole. The unstable of jet boundary layer by receiver wedge due to parameter mismatch is an important reason for differential pressure oscillation in receiving hole.