Biofilm　nitrification　and　activated　sludge　denitrifying　phosphorus　removal　performance　were　investigated　in　the　pre-A2　NSBR　system,　which　treated　real　low　carbon　to　nitrogen　(C/N)　ratio　domestic　sewage.　The　effect　of　organic　substance　and　NO2　--N　concentration　on　the　biofilm　nitrification　performance,　and　different　electronic　acceptors　on　the　denitrifying　phosphorus　uptake　rate　were　studied.　Results　indicated　that　nitrification　rate　was　11.3　mgNH4　+-N/(L•h),　the　ammonia　volume　loading　was　0.27　kgNH4　+-N/(m³•d)　under　the　filling　rate　of　40%,　the　nitrification　performance　was　inhibited　by　organic　substance,　but　the　system　showed　a　good　nitrification　rate　of　9.72　mg　NH4　+-N/(L•h)　when　organics　presented.　NO2　--N　treatment　exhibited　little　effect　on　the　AOB　activity　but　obvious　effect　on　the　NOB　activity,　the　NOB　activity　was　almost　completely　inhibited　(only　1.63%)　when　NO2　--N　concentration　was　400mg/L.　According　to　the　phosphorus　uptake　rate　experiment　under　different　electronic　acceptors,　the　phosphorus　uptake　rate　under　oxygen　and　NO3　--N　was　17.62mg　P/(g　VSS•h)　and　12.94mg　P/(g　VSS•h),　respectively,　anoxic　phosphate　accumulating　organisms　(PAOs)　occupied　73.4%　of　the　total　PAOs,　phosphorus　uptake　performance　was　inhibited　when　the　NO2　--N　concentration　was　30mg/L,　and　phosphorus　uptake　performance　was　inhibited　when　the　NO2　--N　concentration　was　15mg/L　under　the　condition　of　NO2　--N　and　NO3　--N　coexisted.　©　2019,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.