Nitrous oxide (N2O) production during the partial denitrification process with nitrate (NO3-N) to nitrite (NO2-N) transformation ratio of 80% was investigated in this study. Results showed that N2O was seldom observed before complete depletion of NO3-N, but it was closely related to the reduction of NO2-N rather than NO3-N. High COD/NO3-N was in favor of N2O production in partial denitrification with high NO2-N accumulation. It was seriously enhanced at constant acidic pH due to the free nitrous acid (FNA) inhibition. However, the N2O production was much lower at initial pH of 5.5 and 6.5 due to the pH increase during denitrification process. Significantly, the pH turning point could be chosen as a controlled parameter to denote the end of NO3-N reduction, which could not only achieve high NO2-N accumulation but also decrease the N2O production significantly for practical application. (C) 2015 Elsevier Ltd. All rights reserved.