Abstract: Using on-line monitoring equipment for coupled vibration of tandem mill,the signal of drive shaft torque and rolling force were obtained. Regression analysis shows that the neutral angle oscillates at the same frequency in deformation zone. The variation rule of the neutral angle was deduced by using rolling theoretical formula when coupling vibration happens. Then the increment equations for variation of neutral angle caused by rolling vibration were established,and the influencing rules of the variation of deformation zone parameters on the neutral angle were obtained. The results show that effective control of deformation zone parameters can enhance the stability of neutral angle and thus suppress rolling mill vibration.