Abstract: The axle of a shipbuilding gantry crane fractured after 4 years of service, and the fracture reasons were analyzed through field investigation and physical and chemical test. The results show that there were deep machining marks and defects which became fatigue crack sources when bearing large alternating shear stress at the axle shoulder position. Then the cracks tore the surface acicular ferrite and extended to the inside, and finally resulted in the fracture of the axle.