Abstract: Online dynamic characteristics of motorized spindle, an crucial functional component of a machine tool, vary due to the change of its boundary conditions.Therefore, the investigation of dynamic characteristics of motorized spindle is of more significance in engineering domain.In this paper, the dynamic characteristics of combined"Shaft-Bearing"system are studied with the constrained boundary condition theoretically and experimentally, which aims at investigating both the influence of motorized spindle structural characteristics and its assemble procedure.The transfer function of spindle nose calculated by finite element method is verified by constrained experimental modal analysis.It is shown: the analysis model and the experimental platform constructed in this paper are reliable, which can reflect the online motorized spindle dynamic characteristics accurately.The frequencies of first bend mode, obtained by analysis model and experimentation respectively, exactly coincided with each other, and so are the frequencies of second bend mode.The relative error is around 0.57%.The transfer function curve obtained by analysis model and experimentation coincide with each other.The model, as well as the test platform, constructed in this paper can effectively predict the online dynamic characteristics of machining center motorized spindle, which can be regarded as the basis for both further artificial optimization design of motorized spindle and system vibration error analysis-diagnosis-prediction.