Abstract: The high speed motorized spindle system of large computer numerical control (CNC) gear grinding machine tools generates a large amount of heat during the processing, which causes the corresponding thermal deformation of the spindle and grinding wheel, affects the machining accuracy. To solve this problem, a transient thermal-structural coupled analysis method was proposed with thermal contact resistance (TCR) been taken into account. Based on the fractal theory, the W-M fractal function was used to characterize the contact state of the combined surface and the fractal parameter is identified using the root mean square measurement method, the total thermal contact resistance was calculated in combination with the bulk resistance and the constriction resistance. The heat of heat source and the convection heat transfer coefficient of each component were calculated, a comprehensive finite element model was established with consider internal heat source, boundary condition and thermal contact resistance. Thermal error simulation results were obtained. The variation of spindle temperature and thermal deformation was analyzed when thermal contact resistance was taken into consideration. Finally, the thermal error measurement platform of motorized spindle system was established, and the accuracy and reliability of the method were verified. Simulation results show that the temperature and thermal displacement were basically coincide with the experimental data.