Abstract: Mixed crystal defects in gear have a significant impact on the performance and service life of gear. Therefore, for the problem of macroscopic mixed crystal phenomenon occurred in 17CrNiMo6 steel warm forging planetary gear after carburizing and quenching, the mixed crystal samples by three kinds of heat treatment processes were tested to explore the method of eliminating mixed crystal defects. The results show that the fine grain area corresponds to the area with large strain during the forging process, and the strain gradient and overall strain affect the distribution of mixed crystal grains. After isothermal normalizing treatment, the microstructure is a uniformly distributed ferrite+pearlite, which improves the uneven strain and microstructure introduced by forging. After high-temperature austenitization treatment, the grains are refined compared with the original state, but there is still some mixed crystal phenomenon, the average grain size reaches 13.5 μm, and the uneven factor is 2.79. Double quenching treatment can eliminate mixed crystal defects quickly and efficiently, the average grain size reaches 10.6 μm, and the uneven factor is 2.54. The research results show that the appearance of macroscopic mixed crystal defects is related to uneven strain, and the phenomenon of mixed crystal inheritance can be eliminated by heat treatment.