In　this　study,　the　effect　of　nitrite　on　N2O　reduction　during　denitrification　using　external　carbon　sources　was　investigated　in　batch　tests.　The　results　showed　that　N2O　accumulation　grew　with　increase　of　the　initial　nitrite　concentration　at　levels　of　5.92~35.23　mg/L.　Specially,　when　NO2--N　was　35.23　mg/L,　the　N2O　produced　accounted　for　46.26%　of　the　total　reduced　nitrite.　By　contrast,　the　N2O　accumulation　during　denitrification　was　attributed　to　the　decrease　of　specific　reduction　rate　due　to　the　synergistic　reactionof　the　free　nitrous　acid　(FNA)　inhibition　and　the　electron　competition　between　N2O　reductase　and　nitrite　reductase.　These　findings　suggest　that　the　N2O　emission　control　could　be　achieved　by　decreasing　nitrite　concentration　through　the　operation　optimization.　Moreover,　N2O　could　be　used　to　oxidize　methane　for　increasing　energy　production　by　37%　and　reducing　N2O　emission,　which　could　be　achieved　by　increasing　nitrite　concentration　via　nitritation.