Abstract: Based on the analysis of the independently developed MRI-guided needle-penetrating robot, a pneumatic control system is designed. The on/off valve-cylinder model, cylinder friction model and long transmission lines model are established. Then, a fuzzy PID (proportional-integral-derivative) controller is designed, and PWM (pulse width modulation) signal is decomposed linearly. Simulation and experimental results indicate that the controller is effective in both position control and trajectory tracking. The controller is implemented on the robot to verify the needle precision, and the results show that the error of needle penetration is 0.79mm, which meets the accuracy requirement.