Using　domestic　wastewater　as　influent　and　carbon　fibre　as　biological　carriers,　the　characteristics　of　SND(simultaneous　nitrification　and　denitrification)　process　and　N2O　emission　were　studied　under　different　aeration　intensity　(30,20,10　L/h),　with　the　DO(dissolved　oxygen)　concentration　controlled　at　1.5　mg/L　by　adjusting　the　ratio　of　N2　and　O2.　Hetertrophic　and　nitrifying　bacteria　conexisted　in　the　biofilm,　which　are　located　in　the　outer　and　inner　layers　of　the　biofilm,　respectively.　The　decrease　of　aeration　intensity　was　beneficial　to　the　proliferation　of　the　external　heterotrophic　bacteria.　With　the　aeration　intensity　was　controlled　at　30　L/h　and　10　L/h,　the　removal　efficiency　of　NH4+-N　in　the　SBBR　system　were　more　than　95%　and　79.2%±1.6%,　the　SND　efficiency　was　46.2%±2.6%　and　62.1%±2.3%,　the　N2O　yield　was　6.25%±0.6%　and　2.93%±0.43%,　respectively.　During　the　anoxic　phase,　the　denitrification　process　and　the　accumulation　of　PHA　(poly-β-hydroxyalkanoate)　occurred　simultaneously.　In　the　following　aerobic　process,　the　PHA　increased　first　and　then　decreased,　which　indicated　that　PHA　could　be　used　as　internal　carbon　sources　in　the　following　denitrification　process.　Both　the　aerobic　denitrification　process　of　AOB　and　the　denitrification　process　of　denitrifying　bacteria　at　the　presence　of　lower　oxygen　led　to　the　emissions　of　N2O.　The　decrease　of　aeration　intensity　leads　to　a　decrease　in　hydraulic　shearing　force,　an　increase　in　the　anoxic　range　in　the　biofilm,　and　an　increase　in　the　N2O　residence　time　in　the　anoxic　zone,　which　is　beneficial　to　the　denitrification　reduction.　As　the　aeration　intensity　decreased　from　30　L/h　to　10　L/h,　the　extracellular　polymer　(EPS)　secretion　decreased,　and　the　PS/PN　(polysaccharide/protein)　decreased　from　8.59　mg/mg　to　6.58　mg/mg,　resulting　the　reduction　of　the　biofilm　density,　which　created　the　favorable　conditions　for　N2O　transferring　into　the　biofilm　to　complete　the　reduction　process.　©　All　Right　Reserved.