Abstract: The causes of abnormal wear products on brake discs of CRH5 EMU are investigated and analyzed. Through macro and micro inspection analysis, it is found that the abnormal wear products mainly come from the brake disc friction ring. During braking, high temperature is generated between the brake disc and the brake pads, and the metal chips being cut are welded at high temperature. The abnormal wear product gradually grows after multiple braking actions. Analysis shows that the abnormal wear of the brake disc is the result of the extreme cold ice and snow weather, cold welding effect and quenching effect.