Abstract: When the grinding electric spindle was running at high speed, the built-in motor has a large temperature rise, which will have a serious impact on its working performance. Taking the ultra-high-speed grinding electric spindle as the research object, the magnetic thermal analysis of the electric spindle motor was carried out by the bidirectional coupling method. The finite element analysis models of the electromagnetic field and temperature field of the electric spindle were established respectively, and the heat dissipation boundary conditions of the electric spindle and the temperature characteristics of the material were calculated. The electromagnetic loss obtained from the electromagnetic field analysis was imported into the temperature field to calculate the temperature field distribution, and the electromagnetic field material property parameters were changed according to the temperature field to update the electromagnetic loss, so as to realize the two-way coupling analysis of the electromagnetic field and the temperature field. Through the comparison and analysis of the temperature rise experiment results and the simulation results at the end of the winding, it can be concluded that the accuracy of the temperature field analysis of the grinding electric spindle can be improved through the analysis method of the two-way magnetic and thermal coupling.