A　two-sludge　system　combined　anaerobic/anoxic/oxic　with　biological　contact　oxidation　process　(A2/O-BCO)　was　used　to　treat　domestic　wastewater.　By　adding　sodium　acetate　to　adjust　influent　carbon/nitrogen　ratio　(C/N=2.44~8.85),　the　denitrifying　phosphorus　removal　characteristics　of　the　system　were　investigated.　The　results　showed　that　nitrification　performance　(anoxic　denitrifying　loading)　and　poly-β-hydroxyalkanoates　(PHA)　storage　and　utilization　were　mainly　influenced　by　organic　matter,　which　further　effected　the　nitrogen　and　phosphorus　removals.　When　the　influent　C/N　ratio　was　4~5,　COD,　TN　and　PO43--P　removals　reached　to　88%,　80%　and　96%　respectively,　which　achieved　high-efficiency　removal　of　organic　matter,　nitrogen　and　phosphorus　simultaneously.　The　material　balance　analysis　of　carbon　revealed　that　COD　removal　in　the　A2/O　reactor　was　71.86%~77.28%　of　the　total　COD　removal,　and　COD　removal　in　the　BCO　reactor　only　accounted　for　2%~12%,　where　the　efficient　utilization　of　carbon　source　in　the　A2/OBCO　process　was　the　main　reason　to　achieve　deep　denitrification　and　phosphorus　removal　under　the　condition　of　low　C/N.　In　addition,　through　the　correlation　analysis　of　C/N　with　aeration　rate,　nitrate　recycling　ratio　and　anaerobic/anoxic　reaction　time,　the　optimal　operation　strategy　of　the　A2/O-BCO　process　was　proposed.　©　2016,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.