Abstract: Firstly, the structure and function of ankle rehabilitation robot are analyzed. The interdependence of each functional unit of the ankle rehabilitation robot is described. After building the fault tree analysis (FTA) of the ankle rehabilitation robot, and the qualitative and quantitative analysis of FTA, the key parts and failure modes with high relative probability importance are achieved. Then the mathematical model of reliability and reliability block diagram are established. The basic reliability of the ankle rehabilitation robot system is calculated. Thus a more practical and efficient method for reliability prediction in the implementation of rehabilitation robot system is explored, which may serve as the basis for ankle rehabilitation robot reliability design.