In　order　to　meet　the　requirements　of　replenishment　water　in　the　section　of　the　North　Canal　in　Tong-zhou,　Beijing,　the　experiment　was　carried　out　using　pre-denitrification　BAF　and　polyurethane　filler.　The　factors　of　simultaneous　nitrification　and　denitrification　have　been　studied:　gas-water　ratio,　reflux　ratio,　hydraulic　loading　and　filter　height.　When　the　aerobic　section　of　the　gas-water　ratio　was　201,　the　reactor　possessed　obvious　feature　of　simultaneous　nitrification　and　denitrification,　with　the　total　nitrogen　removal　ratio,　of　82.96%,　and　its＇　concentration　in　the　effluent　less　than　the　10mg　/L;　When　the　reflux　ratio　was　11,　anoxic　tank　removal　rate　was　42.3%,　while　aerobic　tank　removal　rate　was　51.85%;　When　the　hydraulic　loading　was　0.32m　3/(m2　h),　the　concentration　and　removal　rate　of　TN　in　the　effluent　were　11mg/L　and　76.67%,　respectively,　at　which　time　simultaneous　nitrogen　removal　rate　of　aerobic　tank　reached　peak.　Sampling　along　the　layer　in　the　aerobic　area,　the　results　showed　that　the　total　nitrogen　removal　mainly　occurred　at　the　bottom　of　the　reactor　ranging　between　0　and　0.6m;　when　DO　is　between　1.5　and　2mg/L,　the　SND　is　obvious,　and　the　TN　removal　rate　remained　above　80%.　By　simultaneously　monitoring　changes　of　ORP　values　along　the　layer,　the　ORP　during　the　simultaneous　nitrification　and　denitrification　process　can　send　control　signal　and　respond　stably　and　sensitively.　According　to　the　changes　of　ORP,　the　aeration　area　can　be　adjusted　efficiently　to　save　energy.　©　2011　IEEE.