In view of the straight travel cylinder controlled valve, the intelligent valve positioner was designed.To study the control algorithm of valve positioner,which was a nonlinear, time varying and unknown model system, asymmetric cylinder pneumatic servo system model was established by using AMESim, which was imported into the corresponding incremental fuzzy selftuning PID control system Simulink model in the form of S function to study models responses of the pneumatic servo system. Comparing two kinds of response characteristics,the results show that the fuzzy selftuning incremental PID controller can improve the response performance of the pneumatic servo system and achieve the goal of the high precision and high speed in the adjustment process.