Operational　performance　of　A2O-BAF　was　investigated　when　treating　domestic　wastewater　with　low　carbon-to-nitrogen　ratio　at　low　temperature.　Under　the　condition　of　average　temperature　of　14.2°C　and　carbon-to-nitrogen　radio　of　4.81,　enhanced　nitrogen　and　phosphorus　removal　was　achieved.　Average　effluent　total　nitrogen　and　total　phosphorus　concentrations　were　13.21　mg/L　and　0.23　mg/L,　respectively.　The　removal　efficiencies　of　COD,　ammonium　nitrogen,　total　nitrogen　and　total　phosphorus　were　86.2%,　99.8%,　96.6%　and　81.5%,　respectively.　The　effluent　quality　could　satisfy　the　first　level　A　criteria　specified　in　the　discharge　standard　of　pollutants　for　municipal　wastewater　treatment　plant　(GB18918-2002).　Although　the　system　was　operated　under　low　temperature,　good　settle　ability　with　SVI　of　85.4　mL/g　was　obtained.　Moreover,　pH　and　oxidation　reduction　potential　could　be　used　as　control　parameters　for　process　control　of　A2O-BAF　system.　It　was　suggested　that　the　operational　state　could　be　well　known　according　to　the　changes　of　simple　online　sensors.