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 hightemperature 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.