Taking a kind of automobile gear monitoring motorized spindle as the research object, based on the optimization design function of finite element analysis software ANSYS Workbench, the shaft overhanging volume, span and the installation position of motor rotor were optimized. After optimization, the spindle radial deformation was decreased by 87%, the axial deformation was decreased by 33%. The factory test showed that at a maximum speed of 2 000 r/min, the noise was only 65 dB, the maximum vibration value was 0456 m/s2.So the optimized motorized spindle can better meet the design requirements, the quality of the spindle is improved.