A stainless-steel hollow needle type anode was used in the reactor to treat industrial wastewater by gas-liquid phase of non-thermal plasma by corona discharge. The results showed that the short electrode gap, 1 cm, has a higher plasma energy density which improves the removal of the phenolic derivatives, reaching 100% after about 60 min. The H2O2 concentration was higher in the discharge system when the content of oxygen was increased. The efficiency of the phenol removal by chemical oxygen demand was only 10–31% after 60 minutes. The identified intermediates were catechol, hydroquinone, 1,4-benzoquinone, 2-nitrophenol, 1,2-benzenedicarboxylic acid, diphenylmethanone, 2-methyl-hydroquinone, 2-methyl-1,4-bezoquinone, and trace amounts of organic.