Previous　studies　have　highlighted　the　salinization　caused　by　the　use　of　seawater　to　flush　toilets　and　industrial　wastewater　entering　the　urban　wastewater　systems　in　coastal　areas.　Thus,　in　this　study,　the　effect　of　salinity　on　N2O　emissions　during　the　partial　nitrification　process,　as　well　as　the　emission　mechanism,　was　investigated　using　a　partial　nitrification　system　of　wastewater　as　the　research　object.　The　results　showed　that　(1)　the　increase　in　salinity　decreased　the　oxidation　rate　of　NH4+　and　the　formation　rate　of　NO2−　during　partial　nitrification;　(2)　the　increase　in　salinity　increased　the　N2O　emissions　during　NH4+　oxidation　and　NH2OH　oxidation　and　decreased　the　formation　rate　of　NO2−-N　during　hydroxylamine　oxidation;　(3)　the　total　N2O　emissions　during　hydroxylamine　oxidation　were　less　than　those　during　ammonia　nitrogen　oxidation,　and　a　greater　amount　of　NO2−　was　reduced　to　N2　instead　of　N2O　during　hydroxylamine　oxidation;　and　(4)　a　novel　finding　was　that,　during　partial　nitrification　with　the　available　organic　matter,　the　N2O　emissions　via　heterotrophic　denitrification　by　heterotrophic　bacteria　should　not　be　ignored,　and　the　increase　in　salinity　can　increase　the　N2O　emissions　generated　via　heterotrophic　denitrification.　These　results　would　provide　a　theoretical　basis　for　reducing　the　N2O　emissions　in　the　wastewater　treatment　process.　©　2023　by　the　authors.