Abstract: Using a small number of thermal key points to build an accurate model of thermal errors has been one of the difficulties in modeling thermal errors in CNC machine tool spindle systems.Taking a gantry milling machine as the research object, this paper analyzed the temperature field, thermal stress, thermal mode and thermal deformation of the machine tool spindle system by finite element simulation method, and three thermal key points were selected on the spindle system according to the simulation results. Then, the temperature change of the thermal key points and the thermal deformation of the spindle system along x, y and z directions were measured experimentally. Finally, the thermal errors of the spindle system were established by multiple linear regression model. The results show that the fitting accuracy of the thermal error models in all three directions exceeds 95%, which proves the effectiveness of the thermal key point selection method in this paper.