The　effects　of　7　groups　of　different　influent　C/N　ratio　(2.75,　4.28,　5.7,　6.5,　6.97,　8.08,　11.19)　on　the　removal　efficiencies　of　total　nitrogen,　phosphorus　and　COD　as　well　as　the　sludge　settling　performance　were　investigated　in　a　UniFed　SBR　lab-scale　apparatus　treating　actual　domestic　wastewater.　The　results　showed　that　when　the　C/N　ratio　was　lower　than　5.7,　TN　removal　efficiency　increased　sharply　as　C/N　ratio　increased,　from　43.6%　of　2.75　to　80.84%　of　5.7.　Afterwards,　TN　removal　efficiency　increased　very　slowly　as　C/N　ratio　increased,　because　only　TN　removal　efficiency　caused　by　SND　during　aeration　period　could　be　enhanced.　P　removal　efficiency　increased　as　C/N　ratio　increased,　because　PAOs　could　get　more　organic　carbon　source　from　the　influent　to　produce　PHB　and　release　PO43-,　avoiding　the　adverse　influence　of　NOx-　on　PO43-　release.　The　higher　the　C/N　ratio,　the　more　the　quantities　of　P　release　and　uptake,　the　quicker　P　uptake　rate,　the　better　P　removal　performance　was.　Regardless　of　the　C/N　ratio,　excellent　COD　(average　93.15%)　removal　efficiencies　were　maintained　throughout　the　experiment.　When　Influent　C/N　ratio　was　bigger　than　6.97　and　organic　load　exceeded　0.38　kg/(kg·d),　SVI　rose　quickly　as　C/N　ratio　increased.　Non-silk　bacteria　sludge　bulge　appeared　because　of　low　DO　and　high　organic　load.