Performance of nozzle-flapper servo-valve driven by piezoelectric bimorph is decided in a great extend by the parameters of control system. Proposed a new control method of the integral separate PID for a piezoelectric hydroelectric servo-valve based on working mode of the servo-valve and the need to debug, a digital controller is designed based on the optimal control parameters of control system of the servo valve. The control effect is investigated through experiments, and how control parameters effecting on performance of servo-valve is analyszed. Response time of servo-valve is less than 6ms when the proportion coefficient is 5.3, integral coefficient is 0.35 and differential coefficient is 3.0. Consequently, it is shown that the digital controller can meet the needs of designing and improving the servo-valve. 