It is difficult to model the thermal error of motorized spindle accurately, and most researches just focus on the axial thermal error and ignore the radial thermal error. Therefore, a method for establishing the model of thermal error is proposed by using thermoelastic theory and mean-value theorem of integral of temperature field. The bearing temperature-thermal deformation model of the motorized spindle is formulated by using the thermoelastic theory. Then, the mean-value theorem of integral is used in the axial thermal error modeling. Therefore, a linear model of spindle temperature and axial thermal deformation is obtained, and the elongation of the end of the spindle could be achieved only by measuring the temperature of key points. The mechanism of radial and axial errors generation of the motorized spindle is analyzed to get the coupled thermal error model. A novel method for measuring thermal error of the motorized spindle by using a ballbar is presented. The feasibility is evaluated by comparing the error theoretical modeling data with the actual measurement data and the error model is imported into the developed independently external-hanging error compensator. Experimental results show that the thermal error of machining the hole’ s radial-error is reduced by about 73. 5% , which shows that the method is reasonable and effective.