Concentration　of　pollutants　especially　influent　C/N　in　municipal　wastewater　is　higher　in　the　northern　China　than　in　the　southern　China.　Therefore,　it　is　difficult　to　keep　efficient　and　stable　removal　of　nitrogen　and　phosphorus　by　using　conventional　biological　treatment　processes　because　of　the　limitations　and　typical　water　quality　in　the　southern　China.　In　this　study,　a　modified　A/O　step-feed　process　was　operated　at　lab-scale　to　deal　with　the　weak　urban　sewage　and　to　remove　simultaneously　biological　nitrogen(N)　and　phosphorus(P).　Under　the　controlled　conditions:　influent　COD/TN　5.16,　HRT　8.7　h,　SRT　15　d,　MLSS　5.66　g·L-1,　sludge　reflux　ratio　75%,　the　volume　ratio　of　anaerobic/anoxic/aerobic　4:8:10,　DO　1.0-1.5　mg·L-1　in　three　aerobic　zones,　continuous　operation　with　six　inflow　distribution　ratio　150　d,　the　optimal　flow　distribution　ratio　obtained　was　20%:　35%:　35%:　10%,　and　the　values　of　COD,　ammonia　nitrogen,　total　nitrogen,　total　phosphorus　in　effluent　were　33.05　mg·L-1,　0.58　mg·L-1,　9.26　mg·L-1　and　0.46　mg·L-1,　respectively.　These　values　were　up　to　Grade　A　discharging　standard　of　pollutants　for　municipal　wastewater　treatment　plant(WWTP)(GB　18918-2002).　The　majority　of　COD　in　raw　water　was　used　as　carbon　source　of　anaerobic　phosphorus　release　and　denitrification　processes,　and　more　than　74%　of　carbon　sources　was　utilized　effectively.　At　the　same　time,　the　experiment　also　found　that　collaborative　control　of　DO　and　ORP　are　not　only　useful　for　anaerobic　phosphorus　release　but　also　for　anoxic　denitrification　and　aerobic　nitrification.　©　All　Rights　Reserved.