Simulation coking wastewater was used as carbon source to investigate the variations of pH and ORP(oxidation-reduction potential)and NO2--N accumulation during denitrification under different C/N(m(COD)/m(NO3--N accumulation during denitrification under different C/N(m(COD)/m(NO3--N))ratios.Results show that the C/N ratio was 6,9 or 13,the changes of pH and ORP could reflect the variation of NO2--N))ratios.Results show that the C/N ratio was 6,9 or 13,the changes of pH and ORP could reflect the variation of NO2--N accumulation concentration,and could indicate "the maximum points of NO2--N accumulation concentration,and could indicate "the maximum points of NO2--N accumulation"and "the real end points of denitrification"well.When C/N ratio was 2.5 or 17,carbon for denitrification was insufficient or excess,the changes of pH and ORP indicated less effective.The main factors of pH were the production of alkali in denitrification and acids of carbon metabolic intermediates.ORP change was more related with the system NO3--N accumulation"and "the real end points of denitrification"well.When C/N ratio was 2.5 or 17,carbon for denitrification was insufficient or excess,the changes of pH and ORP indicated less effective.The main factors of pH were the production of alkali in denitrification and acids of carbon metabolic intermediates.ORP change was more related with the system NO3--N,NO2--N,NO2--N,COD concentrations.With NO3--N,COD concentrations.With NO3--N+0.6NO2--N+0.6NO2--N as the electronic acceptor of denitrification,revised Nernst Equation could accurately(R--N as the electronic acceptor of denitrification,revised Nernst Equation could accurately(R2>0.80)simulate variation of ORP when C/N ratio was 6,9.However,when carbons for denitrification were insufficient or excess,the model could not give good Fitting(R2>0.80)simulate variation of ORP when C/N ratio was 6,9.However,when carbons for denitrification were insufficient or excess,the model could not give good Fitting(R2<0.80).