The pulsed high-voltage discharge is a new advanced oxidation technology for water treatment.Methyl Orange (MO) dye wastewater was chosen as the target object.Some investigations were conducted on MO decoloration including the discharge characteristics of the multi-needle reactor,parameter optimization,and the degradation mechanism.The following results were obtained.The color group of the azo dye MO was effectively decomposed by water surface plasma.The decoloration rate was promoted with the increase of treatment time,peak voltage,and pulse frequency.When the initial conductivity was 1700 tS/cm,the decoloration rate was the highest.The optimum distahce between the needle electrodes and the water surface was 1 mm,the distance between the grounding electrode and the water surface was 28 mm,and the number of needle electrodes and spacing between needles were 24 and 7.5 mm,respectively.The decoloration rate of MO was affected by the gas in the reactor and varied in the order oxygen ＞ air＞ argon ＞ nitrogen,and the energy yield obtained in this investigation was 0.45 g/kWh.