Abstract: The surface metal peeling failure happened to the spiral bevel gear of a rubber plant glue agitator gearbox. The causes of surface metal peeling of the gear were analyzed by macroscopic inspection, medium composition analysis, material composition analysis, hardness test and metallographic examination. The results show that the excessive water content of lubricating oil was the main cause for the surface metal peeling of the gear. The excessive water content reduced the viscosity of the lubricating oil, and increased the friction force between the gears. Contact fatigue stress during gear operation caused the pit formation and metal peeling. Suggestions on acceptance and maintenance of gearboxes and gears were put forward for the metal peeling reasons.