The oxidative degradation of phenanthrene in water induced by the plasma that was generated in a localized zone between an electrolytic solution and a tip of a anode was investigated. Various influence factors such as initial concentration of phenanthrene, applied voltage, initial pH and the catalysts were examined. The results suggested that higher applied voltage was favorable to the removal of phenanthrene. However too high voltage does not significantly improve the removal efficiency, and the co-existence ion of Fe²⁺ had a remarkable catalytic effect on the degradation. By determining the intermediate products of the degradation and by considering the kinetic effect, a reaction pathway was proposed. In which the degradation includes three steps: hydroxylation of the phenanthrene rings, the breaking of the phenanthrene rings and the further oxidation process. Hydroxyl radicals might be the most likely oxidants in the whole oxidation process.