Abstract: A new design method for pressure control system,including the flow force of nozzle-flapper type pneumatic servo valve,is proposed.Calculation method of flow force and linear model of differential pressure control system are established.Based on this model,a PID controller and a disturbance observer are designed using numerical calculation method.The pressure control system can be designed optimally and its controllability could be improved for the reference input tracking and disturbance restraining including the flow force.Good agreement between simulation and experimental results showed that the proposed model is correct.