For the problems such as the asymmetrical structure of upper and lower rollers, different side clearance changes and strip inlet thickness fluctuation for a hot rolling mill, the horizontal-vertical coupled asymmetric nonlinear vibration model under the influence of dynamic rolling forces was established. On the basis of the analysis of inherent characteristics and displacement response, the influences of the change of strip inlet thickness fluctuation, the side clearance change of upper and lower rollers and the change of friction force on the mill vibration and vibration asymmetric amplitude and frequency characteristics were investigated, and it is found that reducing the asymmetry of mill structure and the strip inlet thickness fluctuation, reducing the side clearance of upper and lower rollers and the friction force simultaneously, and the side clearance difference of 3/4 cycle between upper and lower rollers were conductive to improving the stability of rolling mill. Finally, through the study on the bifurcation behavior under the side clearance change of upper and lower rollers, it is found that the side clearance change of upper and lower rollers was not synchronized, which makes the vibration system enter a non-synchronous chaotic state. Thus, the research results provide a reference for the rolling mill vibration suppression theory.