Abstract: In order to reveal the cause of the severe wear, sparking and unstable excitation current of the carbon brush/collector ring on hydroelectric generator, the carbon brush/GCr15 ball pair was used to simulate its contact and friction condition on the Anton Paar Tribometer multi-functional friction and wear tester. Then the effects of load, speed and current density on the tribological properties of the carbon brushes (D172, E468e) under the dry sliding condition with current-carrying and without current-carrying were analyzed. The results show that the tribological performance of the carbon brushes with current-carrying was quite different from that without current-carrying. Without current-carrying, the wear rates of D172 and E468e carbon brushes decreased first and then increased with the increase of load. When the minimum value was reached, a large turning point occurred, so that the change trend of the wear rate of the two carbon brushes was “U” shape. Without current-carrying, the wear rate of the D172 carbon brush was much lower than that of the E468e, while opposite result was obtained for current-carrying condition. Without current-carrying, the wear mechanism of D172 carbon brush was mainly abrasive wear accompanied by mild adhesive wear. With current-carrying, in addition to abrasive wear and adhesive wear, the carbon brush was accompanied by oxidative wear. The wear mechanism of E468e carbon brushes was abrasive wear with and without current-carrying. The friction coefficient of D172 carbon brush increased, while the friction coefficient of E468e carbon brush increased slowly and then gradually decreased. The effect of current on the friction coefficient was obvious for D172 carbon brush but not obvious for E468e carbon brush.