A new stepped variable gap magnetorheological damper (MRD) based on lower limb prosthesis was designed for the issue of different magnitudes of damping force required for gait changes.Based on the Bingham model,the two-step damping gap width and main structure dimensions of the MRD were designed,the internal magnetic field distribution was analyzed by ANSYS Maxwell,and the output damping force was simulated by Simulink.The results show that the maximum operating current of the MRD is 0.4 A,its operating gap is 1.6 mm and its maximum damping force is 902.7 N when walking;the operating gap is 0.6 mm and maximum damping force is 2 033.7 N when running and other complex gaits,which can meet the damping force requirements of different gait.The stepped variable gap MRD has the advantages of graded damping force output,large adjustable range,and low energy consumption,and it can be used in prosthetic systems instead of conventional MRD with fixed damping gaps.