The highprecision aerostatic motorized spindle was taken as the research object, the application characteristics of the three structure types (the “T” type, the “工” type and the “中”type )were introduced. The modal analysis of the three structure types were carried out with the SolidWorks software，and the results were compared with the ones of the Ansys software.In the modal analysis,the effects of the structure type and the axial stiffness on the rotor characteristics were studied.The result shows that the calculation precision of the SolidWorks software can meet the demand of the theoretical analysis of motorized spindle structure design,improving the axial stiffness is able to improve the modal values,especially the second and the third order modal values,and the same working condition,the“工”type motorized spindle has higher modal values than the other two types.