By　treating　real　domestic　sewage　which　is　low　C/N　in　A/O　process　results　showed　that　different　removal　rate　occured　under　different　HRT　of　anoxic　area　without　external　carbon　source.　It　was　demonstrated　that　when　F/M　was　0.28kg/(kgMLSS.d)　and　the　HRT　of　anoxic　area　increased　to　3.04　h　from　2.33h,　both　TN　and　COD　removal　rates　increased,　especially　total　nitrogen　removal　rate　increased　obviously　by　14.11%,　COD　enhanced　by　6.34%.