Abstract: With two antagonistic pneumatic muscle joints in series, a 2-DOF (degree of freedom) leg mechanism is designed, and the Lagrange dynamics model of the single leg is developed based on the pneumatic muscle model with three factors. The system state space is established, and the sliding mode control (SMC) law based on the upper bound of the interference is designed. The simulation and experimental platforms are built. Simulations and experiments of position tracking for hip and knee joints are completed with PID (proportional-integral-differential) control and SMC. The experimental results show that compared with PID control, the position errors of hip and knee joints are reduced by 26.2% and 25.1% respectively under SMC. So, the position tracking accuracy of SMC is better than PID control. The experiment is carried out on the self-developed platform of quadruped robot, which can realize the trot gait under SMC control.