A lower-limb exoskeleton system actuated by compound tendon-sheath artificial muscles is designed and its precise motion control is studied. Firstly, the lower-limb exoskeleton system actuated by compound tendon-sheath artificial muscles is introduced. A transmission model of the compound tendon-sheath artificial muscle is established, and the dynamic model of the lower-limb exoskeleton is then built using the Lagrange method. On this basis, a sliding mode control method is proposed. The motion control of the knee joint of the exoskeleton by the sliding mode control is compared with the proportional-derivative (PD) control, which proves the improved control accuracy of the sliding mode control method. Finally, the passive rehabilitation training experiment is accomplished, and the tracking error of the joint angle is less than 3.78°.