Abstract: In cathodic plasma arc discharge degradation technology, arc discharge is produced in liquid after applying high voltage on the cathode electrode, to rapidly decompose organic molecules in wastewater. After applying a range of high voltages to solutions containing electrolytes (Na₂SO₄, K₂SO₄, NaCl/KCl) at varied concentrations, high performance liquid chromatography (HPLC), ultraviolet and visible spectrophotometry were performed to follow degradation of methyl violet dye in wastewater．Degradation of methyl violet was found to be slowed by \rmSO_4^2- binding to reactive particles released by arc discharge．Degradation became significantly faster with increasing Cl⁻ concentration．At Cl⁻ 0.05 mol·L⁻¹, degradation was complete (100%) within 1 minute, largely due to synergy of arc discharge and presence of high concentration of Cl⁻．