The　experiment　investigated　the　nitrous　oxide　production　under　different　C/N　ratios　during　denitrification,　taking　nitrate　and　nitrite　as　electron　acceptor　respectively.　Ethanol　was　selected　as　carbon　source.　The　C/N　ratios　were　0,　1.2,　2.4,　3.5,　5.0　and　20　when　nitrate　was　taken　as　electron　acceptor　and　C/N　ratios　0,　1.8,　2.4,　3.0,　4.3,　5.2,　6.6,　20.6　when　electron　acceptor　was　nitrite.　The　results　indicated　that:　the　optimum　C/N　ratio　was　3.0　taking　nitrite　as　electron　acceptor　and　the　N2O　production　was　0.044　mg·L-1;　the　optimum　C/N　ratio　was　5.0　taking　nitrate　as　electron　acceptor　and　the　N2O　production　was　0.135　mg·L-1　which　was　3　times　higher　than　that　of　nitrite　as　electron　acceptor.　Though　the　electron　acceptor　changed,　the　trend　of　N2O　production　was　similar:　when　carbon　source　was　badly　insufficient,　the　production　of　N2O　and　denitrification　rate　were　both　quite　small;　the　N2O　production　increased　with　the　increasing　of　the　quantity　of　carbon　source;　when　the　carbon　source　was　excessive,　the　N2O　production　sharply　raised.　Consequendy,　compared　to　complete　nitrification　and　denitrification,　short-cut　nitrification　and　denitrification　could　save　40%　carbon　source.　Moreover,　controlling　C/N　=　3　could　reduce　the　production　of　N2O　in　short-cut　nitrification.