To solve the problem that the impact of the actuator is large when the flexible nozzle hydraulic system of wind tunnel switches from lock state in high pressure to zero condition in low pessure, the pressure relief control loop is added to improve the system. The system simulation mode before and after improvements are established based on AMESim to simulate the working process and then genetic algorithm is used to optimize the relief time. Results show that the optimized model can effectively reduce the impact of actuator while saving energy.