Abstract: Field testing indicates that a rolling mill presents a strong torsional vibration because the load harmonic frequencies are close to the natural frequency of the main drive system during the rolling process. Using field parameters to construct a computer simulation, it is obtained that the load harmonic torque results in motor speed oscillation. At the same time, the motor speed oscillation will excite the motor, causing it to output electromagnetic torque of the same frequency under the effect of the electromechanical coupling. When the load harmonic torque and electromagnetic torque, whose vibration frequencies are close to the natural mechanical frequency, act on the both ends of main drive system for the rolling mill, the main drive system will demonstrate a strong torsional vibration. Finally, the simulation results verify the existence of the vibration and lay a theoretical foundation for vibration suppression.