For　municipal　wastewater　treatment,　a　continuous　anoxic/aerobic　system　(A/O)　combined　with　flow　separate　filler　was　developed　to　investigate　nitrogen　removal　performance.　A/O　was　running　stably　for　113　days　under　oxygen-enriched　condition　(dissolved　oxygen,　DO＞1.5　mg·L-1).　Removal　of　ammonia　nitrogen　and　total　nitrogen　reached　50%,　while　nitrite　and　nitrate　were　not　accumulating　during　the　stable　process.　Simultaneous　nitrification　and　denitrification　was　obvious　in　the　aerobic　zone.　16S　rDNA　results　showed　that　functional　bacterias　were　aerobic　denitrifying　bacteria　(ADB)　in　the　biofilm　of　the　aerobic　zone,　and　FISH　results　showed　the　activities　of　ADB　along　the　aerobic　zone.　Aerobic　denitrification　was　the　main　form　of　simultaneous　nitrification　and　denitrification　in　the　system,　consuming　nitrite　and　nitrate　from　nitrification.　A　nitrogen　removal　pathway　model　via　simultaneous　nitrification　and　denitrification　in　the　biofilm　under　oxygen-rich　water　environment　was　established.　©All　Rights　Reserved