Taking　municipal　waste　water　as　treatment　object,　a　step　feeding-multistage　A/O　process　for　nitrogen　removal　was　conducted.　Furthermore,　the　aim　of　this　paper　was　to　research　growth　characteristic　of　Tubificidae,　and　its　affection　to　nitrogen　removal　and　sludge　charactenstics.　After　120　days　operation,　a　good　performance　was　achieved　in　the　system.　The　COD,　NH4+-N　and　TN　removal　efficiency　was　84%,　100%　and　70%-80%,　respectively.　Three　above　indexes　could　meet　Standard　A　of　Level　1　in　＇Discharge　Standard　of　Pollutants　for　Municipal　Wastewater＇　(GB18918-2002).　It　was　found　that　low　DO　concentration　was　unfit　for　tubificidae　growth,　and　the　mature　Tubificidae　required　more　facultative　space　than　the　larvaes　in　the　long-time　operating　process.　Tubificidae　growth　didn＇t　affect　the　removal　ability　of　the　system.　And,　it　could　increase　the　sludge　sedimentation　performance　and　promoted　sludge　reduction　in　a　certain　degree.