This　paper　was　based　on　Carrousel　oxidation　ditch,　which　was　common　in　the　urban　sewage　treatment　plants.　With　the　effect　of　SND　in　the　oxidation　ditch,　it　was　accomplished　the　effective　removal　for　nitrogen　and　phosphorus　of　urban　sewage　with　low　C/N,　while　adopting　point-aeration　and　brush　flow,　combining　with　the　operation　parameters　adjustment.　Under　the　condition　of　low　dissolved　oxygen　(DO),　the　phenomenon　of　simultaneous　nitrification　and　denitrification　was　obvious　in　macro　and　micro　environments.　And　compared　with　the　traditional　process,　this　process　increased　the　proportion　of　organics　up　to　51%　in　the　ditch,　which　raised　utilization　rate　of　organics.　Based　on　this　to　establish　the　kinetics　model　of　TN　removal,　it　could　control　the　concentration　of　TN　in　the　effluent　effectively　by　adjusting　HRT,　MLSS　and　other　parameters　in　the　oxidation　ditch,　which　would　provide　effective　theory　basis　for　optimization　and　adjustment　of　the　process