A　novel　two-sludge　process　of　A2/O-biological　contact　oxidation　(A2/O-BCO)　is　proposed.　Stable　and　efficient　denitrifying　phosphorus　removal　can　be　realized　by　high-efficiency　utilization　of　influent　carbon　sources　in　the　A2/O　reactor　with　the　electron　acceptors　of　NOx--N　in　the　BCO　reactor.　The　denitrifying　phosphorus　removal　characteristics　of　the　A2/O　reactor　under　different　volume　ratios　(anaerobic　zone/　anoxic　zone/　aerobic　zone)　with　real　domestic　wastewater　were　investigated.　The　results　show　that　the　system　exhibits　good　stability　for　organic　matter　removal,　and　the　variation　of　the　volume　ratios　has　little　effect　on　COD　(chemical　oxygen　demand)　removal.　When　the　volume　ratio　is　241,　the　effect　of　nitrogen　and　phosphorus　removal　is　high,　the　effluent　TN　and　PO43--P　concentrations　being　13.41　and　0.28　mg/L　respectively.　The　nitrogen　balance　analysis　results　show　that　the　phenomenon　of　simultaneous　nitrification　denitrification　(SND)　exhibits　in　the　BCO　reactor,　and　the　occurrence　of　anaerobic　ammonia　oxidation　(Annamox)　contributes　to　the　nitrogen　loss.　Additionally,　the　aerobic　zone　of　the　A2/O　reactor　plays　an　important　role　in　keeping　stable　effluent　PO43--P　concentration.　In　order　to　prevent　secondary　phosphorus　release,　the　NOx--N　concentration　in　the　middle　settler　should　be　controlled　to　1.95　to　2.75　mg/L.　©,　2015,　Southeast　University.　All　right　reserved.