Abstract: An orthogonal experiment (L₂₅5⁶) was designed to have initial pH of the solution, initial concentration of 3,3′,4,4′-tetrachlorobiphenyl (PCB77), dosages of nano zero-valent iron (Fe⁰) and nano zero-valent silicon (Si⁰), and concentrations of humic acid cyclodextrin as affecting factors to study effects of the factors on residual rate of PCB77, concentration of hycrogen ions and changes in redox potential and their relationships. Results show that when initial pH of the solution was at 4.5, initial concentration of PCB77 1 mg•L^-1, dosage of Fe⁰ 10 g•L^-1, concentration of humic acid 0.25 g•L^-1 and cyclodextrin 1 g•L^-1, the residual rate of PCB77 was the lowest (35.2%) after 2 h of reaction. Initial pH of the solution had the greatest influence on PCB77 residual rate, and was followed by dosage of Fe⁰. Initial pH of the solution had the greatest influence on hydrogen ion concentration, too, and was followed by dosage of cyclodextrin. And initial concentration of PCB77 had the greatest influence on oxidation reduction potential, and was followed by dosage of Fe⁰.