The chemical oxygen demand(COD) for pure water and nitrobenzene waste water sample containing different content of H₂O₂ was measured and the linear interference of H₂O₂ concentration on COD test was studied. It shows that with increase of the H₂O₂, the COD increases. Without new interference, the ways to suppress interference of H₂O₂ on COD test were discussed including pH value, manganese dioxide catalyst, and catalase. Results show that the catalase eliminates the influence of H₂O₂ on COD determination effectively, and the alkaline environment is in favor of removing the H₂O₂ to some extent, and manganese dioxide catalyst can remove H₂O₂ in short time but it may introduce new interferences. When the reaction time is 3 min, by adjusing initial liquid pH value of 12, adding manganese dioxide catalyst and catalase, respectively, the H₂O₂ removal rate can reach 1.2%, 45.6% and 100%, indicating that catalase can conveniently remove H₂O₂ with unknown concentration, and suppress the interference of H₂O₂ on COD test.