The　A2N2-SBR　(anaerobic/nitrification/anoxic/nitrification)　double　sludge　system　was　investigated　by　using　low　C/N　domestic　sewage.　This　study　focused　on　the　characteristics　of　nitrifying　bacteria　biofilm　membrane　and　denitrifying　phosphorus　accumulating　bacteria　(DPAOs)　domestication　and　cultivation,　A2N2　double　sludge　denitrifying　phosphorus　removal　process　denitrification　and　phosphorus　removal　characteristics　of　the　startup　process.　The　results　showed　that　by　connecting　sludge　to　A2/O-SBR　unit　and　N-SBR　unit,　respectively　to　culture　domestication　phosphorus　accumulating　bacteria　sludge　and　nitrifying　bacteria　biofilms　separately.　By　using　the　A2/O-SBR　unit　effluent　as　the　influent　of　N-SBR　nitrifying　units,　the　nitrification　biofilm　was　grown　up　successfully　within　25　d.　The　ammonia　nitrogen　removal　rate　was　stable　above　93%.　In　the　A2/O-SBR　unit,　the　sludge　mixture　was　operated　under　anaerobic/aerobic　(A/O)　condition　firstly.　Then,　the　activated　sludge　was　conducted　under　anaerobic/anoxic　(A/A)　condition,　which　reinforced　the　effect　of　the　inoculating　sludge　denitrifying　phosphorus　removal　commendably.　After　43　d,　the　denitrifying　phosphorus　accumulating　bacteria　(DPAOs)　was　successfully　enriched.　DPAOs　accounted　PAOs　for　67.81%.　The　denitrifying　phosphorus　removal　rate　steadily　stayed　above　77.9%.　After　startup　successfully,　about　73%,　13%　COD　of　raw　water　was　used　by　phosphorus　accumulating　bacteria　during　the　A2/O-SBR　unit　anaerobic　phase　and　was　removed　in　the　N-SBR　unit　aeration　process,　respectively.　The　A2N2　system　effluent　COD,　NH+4-N,　PO43--P,　TN　concentrations　was　40.6,　0,　0.4　and　13.5　mgL-1,　respectively,　meeting　national　level　A　emission　standards.　It　was　suggested　that　A2N2　double　sludge　system　denitrifying　phosphorus　removal　process　with　good　denitrification　and　phosphorus　removal　performance.　©　All　Right　Reserved.