Actual　domestic　sewage　was　treated　by　SBR　process　operating　in　Anoxic/Oxic　pattern.　Limited　filamentous　bulking　was　induced　by　low　dissolved　oxygen　at　normal　temperature,　and　SVI　was　maintained　150-220　mL/g.　Occurrence　of　limited　filamentous　bulking　and　growth　of　microorganism　were　researched,　as　well　as　optimization　of　nitrogen　and　phosphorus　removal.　Results　showed　that　filamentous　bacteria　that　led　to　limited　filamentous　bulking　were　H.　hydrossis,　0803　type,　and　M.　parcicella,　which　were　the　dominant　filamentous　bacteria　by　the　biggest　percentage.　It　was　discovered　that　during　phase　of　low　dissolved　oxygen,　removal　rate　of　NH4+-N　decreased　significantly,　from　above　95%　to　65%,　with　obviously　less　PO43--P　and　a　little　higher　COD　in　effluent.　Removal　rates　of　NH4+-N　and　TN　were　greatly　improved　to　above　95%　by　new　operating　pattern　of　Anaerobic/Oxic/Anoxic:　transient　inlet　→　anaerobic　stir(0.75　h)　→　aeration(5　h)　→anoxic　stir(2.25　h)　→settling,　drainage(1　h).　So　efficient,　simultaneous　removal　of　nitrogen　and　phosphorus　was　realized　in　system　of　low　dissolved　oxygen　limited　filamentous　bulking.