Abstract: In order to degrade the organic pollutant in p-nitrophenol wastewater, the effects of operating parameters such as the impressed voltage, pH of inflow, volume of particle electrode, aeration rate and reaction time were examined on PNP and COD_Cr removal rate. The active materials during degradation and degradation pathway were also studied by three-dimensional electrocatalytic oxidation reactor, in which self-made particle electrode was used. The experiment results indicated that the degradation efficiency of PNP increased with the impressed voltage but the gap was closed when the impressed voltage was up to a certain degree. In addition, the degradation efficiency of PNP rose first and then fell with the decreasing of the inflow pH, the addition of the particle electrode's volume and the gradually rise of the aeration. When the impressed voltage was 5 V, initial pH was 5, the mass concentration of particle electrode was 200 g/L and the aeration rate was 0.5 L/min, the PNP and COD_Cr removal rate reached 99.0% and 90.6% after 75 min. Besides, by comparing the degradation efficiency of PNP of the two-dimensional electrochemical oxidation to the three-dimensional electrocatalytic oxidation process, and by comparing commercial columnar activated carbon to self-made particle electrode system, the treatment of the p-nitrophenol wastewater by the three-dimensional electrochemical oxidation and the self-made partical electrode system were much better. Through curve fitting, the degradation of PNP and COD_Cr in p-nitrophenol wastewater was a pseudo-first-order kinetics which could be represented as ln(ρ_PNP,0/ρ_PNP)=0.090 2 t+0.239 7 and ln(ρ_CODCr,0/ρ_CODCr)=0.065 0 t+0.262 3 respectively. By analyzing the active substances such as free chlorine, ·OH and H₂O₂ and the degradation pathway by UV-vis spectra and FT-IR spectra during the process of the PNP degradation, the main active materials were free chlorine and ·OH. There are few intermediate products and the mineralization rate during electrocatalytic oxidation is high.