Abstract: Cryogenic treatment can improve the wear resistance of materials and so on. As one of the core components of the harmonic reducer, the flexible wheel is prone to wear and fatigue and tooth failure. In view of this situation, the 40Cr Ni MoA medium carbon alloy steel for flexible wheels was cryogenic treated by different processes, and the mechanical properties such as hardness, impact toughness, wear resistance and tensile properties of the specimen after cryogenic treatment were compared and analyzed, and the optimal process group was obtained, and the microstructure was observed by scanning electron microscopy. The results show that compared with conventional heat treatment, after the optimal cryogenic process（i.e. cryogenic temperature is-160 ℃, cooling rate is 5 ℃/min, cold holding time is 120 min, cryogenic frequency is 1 time）,the hardness of the material is increased by 0.58 HRC, the impact toughness is increased by 6.15%, the wear amount is reduced by 36.7%, the tensile performance is improved, and the comprehensive performance is significantly improved. The microstructure analysis shows that cryogenic treatment affects the precipitation behavior of carbides in the sample.