Aiming at characteristics of the lower limb assisted exoskeleton knee joint position servo systems， such as high servo accuracy， large impact torque and wide load range， a sliding mode control strategy of position servo system based on fuzzy rules is proposed. This strategy designs a new type of sliding mode surface with integral terms. The structure of the fuzzy adjustment part is of single input and double output. Fuzzy rules are used to adjust the new terminal sliding mode approach rate to suppress sliding mode chattering. Both experiments and simulations demonstrate that the control strategy has good stability and servo tracking performances， and strong robustness with respect to load disturbances.