Taking　actual　domestic　wastewater　(C/N　=　3.5)　as　influent　substrate　and　carbon　fiber　as　biological　carrier　(filling　rate　of　35%),　the　simultaneous　nitrification　and　denitrification　via　nitrite　was　achieved　in　a　sequencing　batch　biofilm　reactor　(SBBR)　using　limited　DO　concentration　and　intermittent　aeration　respectively　at　normal　temperature　of　(20±2.0).　The　ammonia　oxidizing　bacteria　(AOB)　became　the　dominant　species　in　the　SBBR　in　120　d.　The　＇feast-famine＇　characteristics　of　AOB　led　to　the　rapid　accumulation　of　nitrite　under　intermittent　aeration　conditions.　Most　of　COD　was　taken　up　and　converted　to　polyhydroxyalkanoate　(PHA),　which　was　used　as　internal　carbon　sources　for　the　following　denitrification　process.　Under　the　conditions　of　low　oxygen　(DO=0.5　mg/L)　and　intermittent　aeration,　the　removal　efficiency　of　NH4+　-N　in　both　reactors　was　more　than　95%.　The　yield　of　N2O　was　4.38%　and　3.65%,　the　SND　efficiency　was　77.9%　and　87.1%,　respectively.　The　effluent　was　mainly　NO2-.　Both　the　lower　DO　concentration　and　intermittent　aeration　could　reduce　the　degradation　rate　of　COD,　provide　the　external　carbon　source　needed　for　denitrification,　and　reduce　the　amount　of　N2O　emissions.　The　aerobic　denitrification　process　of　AOB　and　denitrification　process　of　NO-x-N　using　internal　PHA　as　carbon　source　can　promote　the　emissions　of　N2O.　The　anoxic/aerobic　environment　under　intermittent　aeration　conditions　reduced　the　substrate　of　aerobic　denitrification　substrate　and　is　beneficial　to　the　reduction　of　N2O　emission.　©　All　Right　Reserved.