Field investigations have demonstrated that the wear life of a carbon slider of a pantograph in a high-speed train of the 250 km/h speed class is very short. In this study, several experimental tests were performed on a high-speed test machine to understand the mechanisms of the serious wear of the slider against the wire under electric current. The experiments on the high-speed railway were carried out at electric currents of 200, 300, 400, and 500 A, sliding speeds of 100, 150, 200, and 250 km/h, and normal loads of 60, 80, 100, and 120 N. The friction coefficient, wear volume, arc electric current, arc electric voltage drop, and temperature increase of the carbon slider were recorded and analyzed. The experimental results demonstrated that the wear volume of the slider increased with the electric current and that arc melting and thermally enhanced wear were the dominant mechanisms causing the serious wear of the slider.