Abstract: During the fatigue test of the main undercarriage buffer, the upper arm pedestal of the buffer fractured. Through analyzing the chemical composition, hardness and metallographic structure of the pedestal material, the macro and micro morphology of the fracture surface and the energy spectrum of the fracture surface, the fracture characteristics, crack initiation, propagation and fracture process of fracture surface were studied. The results show that under high temperature caused by friction, cadmium ions infiltrated into the matrix to form eutectic, resulting in fatigue source. Under alternating stress, cadmium embrittlement occurred, leading to crack source, and then crack propagation led to fracture. According to the fracture cause and the service environment, it is proposed to adjust the surface treatment process of the arm. The cadmium plating process should not be used for the mating surface. It can be replaced by zinc plating process or other ultra-high-strength steels with strong corrosion resistance can be used.