Boron-doped diamond (BDD) electrodes are promising anode materials in electrochemical oxidation system in degradation of wastewater containing toxic and bio-refractory organic pollutants due to their corrosion resistant ability and strong oxidation ability. In order to further improve the performance of BDD anode system, electrochemical oxidation of p-nitrophenol(PNP) was initially investigated in BDD anode system with the presence of sensing electrode. The results showed that the performance of the synthetic system was improved under neutral conditions with the joint actions of anode oxidation (64.6%) and H₂O₂ which was produced by oxygen reduction at carbon fiber cathode (11.9%). Under acid conditions, the degradation efficiency of PNP was further improved from 41.8% of the traditional system to 84.5% of the synthetic system. The strong oxidation ability was due to the anode oxidation (24.5%) and Fenton reaction by H₂O₂ and Fe²⁺ releasing from sensing electrode (66.7%). Moreover, under alkaline conditions, the results showed that the combined system was also improved by the coagulation of iron flocs formed from sensing electrode besides anode oxidation. Furthermore, hydroxyl radicals and H₂O₂  which were dominated oxidants were detected and quantified for the oxidation mechanism explanation.