The servo system actuated by oscillating pneumatic cylinder for X-Y plate is a multi-variable nonlinear control system. Its mathematical model is established, and nonlinear factors are analyzed. Due to the existence of deadlock zone and the small damp of the pneumatic oscillating cylinder, it is likely to result in overshoot,and there is also certain steady-state error, so online modifying of proportion-integration-differentiation (PID) parameters is needed so as to achieve better control performance. Meanwhile considering the stability demand for long-term run, a fuzzy adaptive PID controller is designed. The result of hardware-in-loop (HIL) test and real-time control experiment shows that the adaptive PID controller has desirable self-adaptability and robustness to external disturbance and to change of system parameters, and its control performance is better than that of traditional PID controllers.