The main drive system of CSP rolling mill abnormal vibration phenomena was analyzed to determine the causes of the vibration. At first, it was found that the mechanical gaps of the main drive system had a great impact on twist vibration of system, and then the rolling interface changes due to rolling torque on the vibration impact was analyzed. The MATLAB/Simulink software was used to simulate the rolling torque. The results show that the fluctuation of the rolling torque has a immediate impact on the vibration of the main drive system. The fluctuation of the friction coefficient impacting the main drive system vibration is due to the steadstate selfexcited torsional vibration produced to the main drive system. By analyzing the electrical parameters controlled by the inverter and the main drive system torsional vibration impact,it concludes that the harmonics torque is generated by the electromagnetic harmonics, so that the main drive system can produce the torsional response. At last, a series of measures on the theoretical basis to inhibit the abnormal vibration were provides.