Abstract: The working environment of high-end gear products such as wind power and high-speed railway is complex and harsh, and the requirements for tooth surface hardness and toughness are high. In case of damage, the maintenance cost is high. In view of the situation, the orthogonal test schemes of magnetic deep cryogenic treatment was designed for18Cr Ni Mo7-6 carburized steel, the optimal process groups were selected for Rockwell hardness testing, and their microstructure and grain size were observed by optical microscope.Compared with the results of conventional heat treatment,the effects of magnetic deep cryogenic treatment on the impact toughness, hardness and microstructure of 18CrNiMo7-6carburized steel were explored. The results show that the impact toughness and hardness are improved after magnetic deep cryogenic treatment. The optimum process parameters are that the magnetic field strength is 1 T, without alternating treatment,the deep cryogenic temperature is-190 ℃, the cold holding time is 16 h, and the cooling rate is 2 ℃/min. The impact toughness increases by 38.07% and Rockwell hardness increases by 9.49% compared with that of the conventional heat treatment. The microstructure analysis shows that the magnetic deep cryogenic treatment can promote the transformation of residual austenite and refine the grains.