Abstract: The vibration of the second finishing mill of a hot rolling line in a domestic steel plant is very severe when rolling thin strip. By establishing the vertical vibration and horizontal vibration finite element model of this rolling mill system, it calculates the multi-step natural frequency of rolling mill system. It also analyzes it comprehensively with the field vibration test signal. The results show that when the motor speed reaches 90-110rpm, the meshing frequency of the gear base is about 16.6-18.8Hz, which is close to the first torsional vibration frequency of the horizontal vibration system, forming forced vibration; when the motor speed reaches 110-120rpm, the meshing frequency of the gear base is 21.4-23.3Hz, which is close to the first axial vibration frequency of the rolling mill, forming forced vibration. The vibration of rolling mill can be effectively reduced by controlling the motor to pass through these two speed ranges quickly.