The contact state between the rotating rail and the track directly affects the arc thermal characteristics of the electromagnetic railgun system, which in turn determines the system’s reliability and service life. To address issues such as gap discharge and arc ablation caused by wear of the rotating rail, this study constructs a finite element model of the rail contact and explores the impact of changes in the metal liquefaction layer thickness, the armature tail wing surface roughness, and the rail gap width on arc energy density, current density, and temperature distribution. The results show that the arc energy density primarily concentrates in the raised peak regions of the rough armature tail wing surface, with the thickness of the metal liquefaction layer having a minimal effect on the arc energy density distribution. Increasing the roughness of the armature tail wing significantly raises the peak value of arc energy density while reducing the current density at the rotating rail contact interface. There is a synergistic effect between the rail gap width and the track surface roughness, which together promote an increase in arc energy density. Additionally, as the gap widens, the impact of track roughness becomes more pronounced. This study reveals the effects of rotating rail contact conditions on arc thermal characteristics, providing theoretical support for arc suppression and structural optimization of electromagnetic launch system.