Abstract: Performance of electric contact between armature and rails（A-R） developed as armature sliding in railgun bore, in which electromagnetic(EM) characteristics at A-R interface was the fundamental mechanism. Based on transient magnetic field calculation of railgun system, effects of three factors including pulse current, armature velocity, local contact area on evolvement rule of EM characteristics at A-R interface were analyzed. Besides, groups of launching experiments were designed to comprehensively verify the evolvement rule of EM characteristics at A-R interface. Analysis results indicated that, variation of pulse current induced tendency of current concentration towards contact front end, and decreased crowding level of surface current peak region. Armature velocity induced tendency of current concentration towards contact trailing end. Crowding level of current contact trailing end became strengthened as armature velocity increased after 50 m/s, at which current distribution on contact surface was the greatest. Mode of current concentration on the contact surface became U style close to the contact trailing end. Compared with entire surface contact, current density peak was enhanced at various local contact situations, but difference became smaller when local contact area increased or armature velocity increased. Under normal magnetic force, initial contact area would be extended forward. Effect rules above are validated through surface detection of rails and armatures after launching experiments. A-R sliding electric contact mechanism will be deeply studied based on this research results.