Lower　extremity　paralysis　tends　to　be　common　in　recent　years,　and　rehabilitation　robots　are　developed　to　help　patients　recover.　In　this　paper,　a　robotic　exoskeleton　is　designed　to　provide　rehabilitation　training　in　two　modes,　including　robot-active　mode　and　human-active　mode.　Magnetorheological　(MR)　actuators　are　manufactured　and　set　in　the　robot.　In　the　robot-active　mode,　the　MR　actuator　works　as　a　clutch　to　transfer　the　torque　generated　by　the　motor　to　the　leg　joint,　providing　flexible　torque　instantaneously　for　human　safety　and　reducing　the　power　consumption.　While　in　the　human-active　mode,　the　MR　actuator　functions　as　a　brake　to　provide　controllable　damping　torque　to　conduct　anti-resistance　training　to　help　patients　strengthen　muscles.　Biomechanical　simulation　based　on　AnyBody　Modeling　System　(AMS)　is　also　analyzed.　Then,　a　human-robot　interaction　control　method　is　proposed,　where　the　effect　of　the　MR　actuators　is　taken　into　consideration,　and　experiments　are　conducted　to　verify　effectiveness　of　the　control　strategy　of　the　robotic　system.　©　2019　IEEE.