Abstract: The driving bevel gear of a forklift fractured during unloading process. The causes of fracture of the bevel gear were analyzed by means of macro analysis, chemical composition analysis, metallographic examination, hardness test, SEM analysis of fracture and so on. The results show that the bevel gear was penetrated hydrogen during the heat treatment carburizing process, which resulted in the segregation of atomic hydrogen at the stress concentration area of the transition steps of diameter ϕ45 mm and ϕ40 mm, where the cracks initiated and expanded. Finally, hydrogen embrittlement fracture occurred to the bevel gear.