When the torsional vibration of the drive shaft of rolling mill is monitored on-line by means of the torquetelemetry system,the signal features show that the electromechanical coupling vibration occurs in the main drivesystem.In order to reveal its mechanism,the harmonic components with fundamental wave in the cycloconverteroutput current and the corresponding harmonic torque are obtained by a Matlab /Simulink simulation,the characteristicsof drive mechanical structure are analyzed by means of ANSYS.Then,an equivalent kinetic model of drive mechanicalstructure with nonlinear stiffness and damping term is built,and the coupling mechanism and characteristicof harmonic excitation and mill structure are revealed. Simulation results indicate that both reducing harmonicamplitude and increasing damping can decrease vibration energy to a large extent.