The　first　level　A　standard　of　the　sewage　discharge　for　phosphorus　removal　could　not　reach　when　only　biological　method　is　employed,　such　as　the　traditional　CAST(cyclic　activated　sludge　technology)　process　that　has　been　widely　used　in　municipal　wastewater　treatment　plants.　A　modification　for　the　traditional　CAST　process　was　made　by　introducing　an　independent　stirring　phase　in　the　main　reactor　zone.　The　modified　process　has　been　demonstrated　in　a　full-scale　wastewater　treatment　plant.　To　optimize　the　metabolic　environment　for　polyphosphate　bacteria　and　to　increase　its　competition　ability,　gradually　the　aeration　time　was　shortened　and　the　anoxic　stirring　time　extended　by　two　stage　experiment.　For　the　modified　CAST　process　the　efficiency　of　phosphorus　removal　is　89.1%,　22%　higher　than　non-modified　CAST　process,　and　the　first　level　A　standard　of　the　sewage　discharge　could　be　steadily　reached　for　the　effluent　TP.　The　results　of　static　tests　showed　that　the　modification　of　process　can　increase　the　proportion　of　denitrifying　polyphosphate　accumulating　organisms,　and　that　the　removal　of　1　mg·L-1　PO43--P　need　consume　of　1.67　mg·L-1　NO3--N.　So,　the　denitrifying　performance　was　also　improved,　and　the　concentration　of　NH4+-N　and　TN　in　effluent　both　could　meet　the　first　level　A　standard　with　10.4%　energy　saved.　©　All　Rights　Reserved.