The thermal erosion of arc is the main cause of electrode loss in the spark gap switch. The graphite electrode will evaporate and constantly undergo mass loss under the effect of the arc, which changes the gas environment in switch and the electrode distance, resulting in decreased reliability of the switch operation. To obtain erosion characteristics of graphite electrode under high-current pulse arc, the energy coupling model between the switching arc and graphite electrode is established based on the switching arc transient diffusion characteristics and graphite material parameters, and the heat transfer characteristics of plasma-solid region is obtained. Considering the phase change characteristics of graphite electrode, the heating range and critical phase change point of graphite electrode under transient thermal effect is calculated, and the phase change mechanism of graphite electrode under transient thermal shock of the arc is studied. The study results indicate that the heat flux of the arc-electrode interface is mainly concentrated in the center of the arc contact surface, and the energy density of arc deposition can reach up to 10⁹ W/m². Graphite is basically in a heating state at the beginning of the current rise, under the effect of energy accumulation, the graphite transforms into sublimation state. The heat transfer intensity decreases sharply with the radius decreasing, and the evaporation radius is slightly smaller than the arc radius. The ablation morphology and mass loss of graphite electrode under five different switching conditions were recorded through experiments. The experimental results show that the electrode mass loss is linearly related to the energy deposited on the electrode surface by the arc, approximately 0.015 mg/J. This paper studies the influence of arc key parameters on electrode mass-loss rate, and provides a theoretical and experimental basis for slowing electrode loss.