Abstract: The cooling fan blades play a crucial role in traction motors, and the complex working environment of traction motors leads to the fan blades fractured. In this paper, the failure mode and causes are analyzed by appearance observation, metallographic examination and hardness testing of the blades, as well as macro-and-micro observation of the fracture surface. The fracture properties and causes of the blades are comprehensively analyzed. The results show that there are welding defect at the end of the vertical plate weld forming the fan blade; At the same time, the blade fractures due to the combined effect of low-cycle centrifugal tensile stress and high-cycle vibratory stress, leading to a mixed low-high fatigue failure. At last, it is recommended to optimize the structural design of the blades in order to enhance the load-bearing capacity of the blades and reduce the vibration stress of the cooling fan; in terms of production process, strictly control the welding quality, and carry out anti-fatigue performance treatment on the blades in order to improve its fatigue resistance.