In the motorized spindle rotor system,the bearing and the pedestal are mainly connected by clearance fit,and the amount of clearance fit will change non-uniformly under the influence of the thermal deformation of the bearing.In order to investigate the influence of the bearing fit clearance change on the vibration characteristics of the rotor system,the dynamics model of the motorized spindle rotor system with consideration of the clearance fit was created.The vibration characteristics of the system were analyzed by using the time domain response and Fourier spectrum,and the influence of bearing clearance fit on the stability of the rotor system was analyzed by combining the bifurcation diagram and Poncalai mapping.Finally,the simulation results were verified by setting up the motorized spindle vibration test bench.The results show that the vibration of the rotor system is enhanced with the increase of the bearing clearance at different rotational speeds,and the stability of the system will be transitioned from the periodic motion to the proposed periodic motion and then into the chaotic state with the increase of the clearance.When the gap is 5 μm,the vibration error between the test results and the simulation results is about 4.18%,which verifies the accuracy of the model.