Abstract: Setting up the preparatory heat treatment process in the manufacturing process of the parts can effectively improve the machining performance of the parts, reduce the internal stress of the workpiece, and provide a good microstructure for the final heat treatment. Firstly, the theory of heat treatment technology for normalizing was discussed, and the phenomenon of surface crack after heat treatment of ZG310-570 marine large size gear was analyzed, the strategy of eliminating the surface crack phenomenon after tempering was studied. The results show that in the two possible effective schemes, the preparation heat treatment combination scheme of high temperature normalizing normalizing tempering is adopted, and the surface crack problem of the batch of large size gear after heat treatment is verified and solved by test.