In　order　to　solve　the　instability　of　removing　nitrogen　and　phosphorus　process　in　A2O,　the　high　effluent　nitrogen　and　phosphorus　concentration　issues,　fluidized　immobilization　media　were　added　to　the　aerobic　reactor　to　maintain　a　high　concentration　of　nitrifying　bacteria　and　nitrification　rate.　The　effect　of　different　carbon　loading,　carbon　sources　and　filing　carbon　modes　on　the　process　of　nitrogen　and　phosphorus　were　studied.　In　addition,　on　the　condition　of　the　low　concentration　ratio　of　COD　to　TN,　the　device　was　modified,　i.e.,　adding　pre-anoxic　period　before　the　anaerobic　zone　so　as　to　reach　the　advanced　nitrogen　and　phosphorus　removal.　The　results　show　that　when　the　influent　concentration　ratio　of　COD　to　TN　is　in　the　range　of　3.6-8.1,　the　COD,　TN　and　TP　removal　rates　change　with　different　nitrification　liquid　reflux　ratio　i.e.,　the　higher　concentration　ratio　of　COD　to　TN　and　the　nitrification　liquid　reflux　ratio,　the　lower　the　effluent　nitrate.　When　the　concentration　ratio　of　COD　to　TN　is　8.1　and　the　nitrification　liquid　reflux　ratio　is　300%,　the　effluent　nitrate　concentration　is　only　4.23　mg/L.　TP　removal　rate　is　low　on　the　condition　of　the　low　concentration　ratio　of　COD　to　TN.　When　the　concentration　ratio　of　COD　to　TN　is　higher　than　4.5,　phosphorus　removal　is　almost　100%.　A2O　system　biofilm　nitrification　is　at　the　percentage　of　total　81.6%,　while　the　activated　sludge　nitrification　accounts　for　only　18.4%,　which　shows　that　the　biofilm　has　good　nitrification　efficiency.