Abstract: The vacuum carburizing oil quenching process was employed in the production process of the driving gear of a heavy haul locomotive in rail transit. The vacuum carburizing process of 18CrNiMo7-6 material for driving gear was studied and compared with the conventional controlled atmosphere carburizing process. After the treatment, the carbon concentration, hardness, effective hardening depth and metallographic structure of the sample wereanalyzed. The vacuum carburizing process can save 18% of treatment time compared with the traditional controlled seven-minute carburizing process. There are no bad microstructure such as inner oxidation and non-martensite after vacuum carburizing. The grade of martensite and carbide meet the technical requirement of the locomotive driving gear.