BACKGROUND A large amount of N2O is often generated in the high-salt wastewater nitrogen removal process, which is unfavorable to the environment, so it is necessary to build a model to describe the N2O production characteristics in high-salt environment. RESULTS This work merges three nitrous oxide (N2O) production pathways, namely ammonium-oxidizing bacteria (AOB) denitrification, incomplete hydroxylamine (NH2OH) oxidation and heterotrophic denitrification, into a multispecies activated sludge model to describe N2O production under salt stress for the first time. The heterotrophic denitrification pathway was divided into two parts, namely denitrification on intracellular polymers and denitrification on endogenous respiration, and high-salt inhibition terms were added to the intracellular polymer expressions on the heterotrophic denitrification pathway. The developed model was calibrated by a cycle running experimental case and validated by three single experimental cases, then assessed by two different sets of experimental data. The results indicated that the model reproduced experimentally measured data from six cases perfectly. The modeling results showed that the heterotrophic denitrification pathway (70.04-81.52%) played a significant role in N2O production, while smaller amounts of N2O were generated by the AOB denitrification pathway (14.53-23.93%) and incomplete NH2OH oxidation pathway (3.54-7.75%). CONCLUSION Denitrification on endogenous respiration will produce a small amount of N2O with an initial carbon source; when there is no initial carbon source, it will be dominant. Owing to the competitive effects of heterotrophic denitrifying bacterial nitrogen reductase on electron donors, N2O conversion (ratio of N2O production to total nitrogen removal) will increase with decreasing carbon source. (c) 2019 Society of Chemical Industry