Abstract: The assembly precision of gears in aero-engine transmission systems is relatively high, yet controlling the deformation of assembly dimensions after heat treatment presents significant challenges. The deformation of parts cannot be effectively controlled after alkali bath free quenching, which seriously affects the assembly and use of gears. This study focuses on the 16Ni3CrMoE steel output gear as the research object, and the key dimensions of the parts are limited to control the deformation of the parts by pressing oil cold quenching instead of alkali bath free quenching. The microstructure, hardness, properties and dimensions of the parts quenched by the two methods are compared and analyzed. The results show that the deformation of the parts can be effectively controlled by the cold-quenching process of the moulded oil, and the machining of the parts can meet the technical requirements.