The invention relates to a lower limb joint rehabilitation training device for passive and active exercise training, which comprises a bottom plate, a leg-placing plate, a rod length regulating button, an adjustable leg bracket, a connecting rod, an adjustable crank, a rigidity variable mechanism, a tensioning connecting sleeve, a bearing block, a bottom plate, a display, a control keyboard, a leg bracket fixing knob, a shank fixing belt, a motor transmission mechanism and a control circuit, wherein the motor transmission mechanism and the control circuit are arranged in a shell. The lower limb rehabilitation training device is characterized in that the rigidity variable mechanism driven by a magnetorheological fluid damping brake is arranged at the center of two inner walls of a leg-placing plate frame, wherein the rigidity variable mechanism comprises an exciting current regulator, an exciting current wire, the magnetorheological fluid damping brake, a support shaft seat, a gear shaft, a gear and a rack. Because the rigidity variable mechanism driven by the magnetorheological fluid damping brake is adopted to replace a rigidity variable mechanism driven by a motor, damping forces are set when different patients make active exercise training; and the invention has the advantages of reasonable design, compact structure, convenience for processing, manufacturing and using, and the like.