The fit of the outer ring of the bearing has a significant impact on the dynamic performance of the bearing and its rotor system. In order to obtain the optimal fit of the outer ring of the bearing, a model for optimizing the fit of the outer ring considering the dynamic characteristics of the bearing is proposed. Firstly, based on Hertz contact theory, a bearing dynamics model considering temperature variation and fit changes is established, and the relationship between the dynamic characteristics of the outer ring contact force bearing is analyzed; Then, an optimization model is established with the radial contact force of the bearing as the objective and the bearing fit as the variable. The model is solved using bilinear interpolation method to calculate the optimal outer ring fit of the bearing. Finally, the dynamic characteristics of the optimized bearing under different working conditions are analyzed and compared. The results show that after optimizing the bearing fit, the vibration of the bearing rotor system is smaller than that under other fit clearances. Through the vibration test of the bearing rotor system, a conclusion consistent with the simulation results was obtained, with an average experimental error of 4.48%. The research results provide a certain theoretical basis for improving the bearing structure and assembly optimization.