Abstract: The wire fractured during the vehicle test of the electric vehicle. The causes of fracture on the wire were analyzed by macro observation, micro observation, metallographic examination and energy spectrum analysis. The results show that the fracture of copper wire of electric vehicle was fatigue fracture. The fixed point of the wire was set unreasonably and the free activities range was too large, resulting in excessive alternating stress on the fixed end of the wire during the vehicle vibration test. After running for a period of time, the wire fatigue fracture near the plug terminal of the fixed point. During the continuous operation of the vehicle, the conductor contacted intermittently, resulting in the high temperature ablation of the fracture of the conductor, and the black covering material was produced on the surface, which was mainly composed of copper oxide.