Abstract: We experimentally addressed the surface ablation of W-Cu alloy(W70) electrodes by discharge arc of high voltage pulse in water.The weight-loss of W-Cu electrode and/or concentrations of metal ions in water were measured,respectively,to understand the ablation mechanism(s).The preliminary results show that the high temperature physical and electrochemical reactions,occurring at the water/electrode interface,all had a major impact.For example,the ablation-rate in water was faster than that in air because of the electrochemical corrosion of WO^2-₄,Cu²⁺,OH^1-,O₃ and H₂O₂ formed in electrolytic reactions.Randomly distributed arc-spots and dominance of Cu/CuO on the surfaces revealed that the arc-induced rapid segregation/melting/evaporation/oxidation of Cu accounted for the ablation mechanisms.The ablation-rate of anode was higher than that of cathode,the former changed in a rapid-steady increase mode and the latter increased steadily.