A method of controlling surplus torque by optimizing mechanical properties was proposed in this study. First, the mechanical structure and operating principle of electric loading systems were presented and a mathematic model was constructed. Then the causes of surplus torque were analyzed and a transfer function was created to relate the angular velocity-induced disturbance to output torque based on the results of analysis. A simulation was conducted in MATLAB to investigate the effects of mechanical properties of the system on surplus torque. The results suggest that proper design of mechanical properties can help reduce surplus torque.