To　study　the　effects　of　influent　ρ(C)/ρ(N)　on　two-sludge　nitrogen　and　phosphorus　removal　system,the　characteristics　of　a　pilot-scale　AAO-biological　aerated　filter(BAF)　treating　about　50　m3　real　domestic　wastewater　per　day　were　investigated　under　ρ(C)/ρ(N)　level　of　3.3±0.3,　4.5±0.3,　and　6.0±0.3,　respectively.　Results　show　that　when　ρ(C)/ρ(N)　is　about　3.3,　the　removal　rates　of　COD,　TN　and　PO4　3--P　reach　71.4%,　67.6%　and　85.6%,respectively.　The　nitrogen　and　phosphorus　removal　performance　of　the　system　reach　the　best　when　ρ(C)/ρ(N)　is　raised　to　4.5　by　adding　organic　matter,　the　removal　rates　of　COD,　TN　and　PO4　3--P　reaching　79.7%,　70%　and　93.5%,　respectively.　The　average　effluent　TN　and　PO4　3--P　are　12.40,　0.20　mg/L,　respectively.　However,　when　ρ(C)/ρ(N)　is　about　6.0,a　large　amount　of　available　organic　compounds　in　the　anoxic　area　result　in　the　rapid　depletion　of　the　electronic　receptor　NO3　--N　by　denitrifying　bacteria,　affecting　the　removal　of　the　nitrogen　and　phosphorus　by　DPAOs.　As　well,　residual　organic　matter　is　found　in　the　BAF,　which　result　that　NH4　+-N　cannot　be　completely　oxidized　to　NO3　--N　because　of　the　proliferation　of　heterotrophic　bacteria.　In　this　situation,　the　removal　rate　of　COD　is　81.6%,　removal　rates　of　TN　and　PO4　3--P　by　AAO-BAF　process　drop　to　55.1%　and　63.2%　rapidly,　and　the　system　is　close　to　collapse.　©　2019,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.