The invention discloses a variable-rigidity ankle rehabilitation orthosis and a motion control method thereof. The variable-rigidity ankle rehabilitation orthosis comprises a puttee, a calf bracket, afoot plate, a variable rigidity magnetorheological elastic driver, a man-machine interaction system, sensors and a control system, wherein the variable rigidity magnetorheological elastic driver consists of a motor element, a magnetorheological brake and a rigidity regulatory mechanism, can regulate the rigidity of the system in a real-time manner, can buffer earth shock and can improve the system energy efficacy and safety; the man-machine interaction system is based on an intelligent terminal application program, is used for assisting in the orthosis, and is used for providing varied interactive functions of orthosis condition monitoring and operation, on-line voice feedback, motion performance summarization and the like. The control method is based on hemiplegic patient walking state analysis and requirements, and functions of driving through the variable rigidity magnetorheological elastic driver, braking, mixed braking, rigidity regulation and the like, and can output anticipantauxiliary moment and motion, so as to realize ankle rehabilitation training of patients.