Abstract: In order to study the influence of high-temperature tempering process on the microstructure of heavy-duty gears in coal mining machines, the volume fraction changes of the microstructure after high-temperature tempering were obtained through experiments. The variation rule of retained austenite content with process temperature and process times after high-temperature tempering was also studied. The results show that with the increase of high-temperature tempering times, the content of retained austenite in the surface layer and transition layer decreases, and the surface carbon concentration also decreases. With the increase of high-temperature tempering temperature, carbides precipitate at grain boundaries, which has a negative impact on performance. Finally, a method of tempering at 650℃ for 2 times is selected as the tempering process after carburizing.