One　lab-scale　biofilter　that　simultaneously　removal　of　Fe,　Mn　and　ammonia　from　groundwater　was　established　to　investigate　autotrophic　nitrogen　conversion　process　and　microbial　population　distribution.　The　results　showed　that　56　d　were　needed　to　achieve　the　required　values　of　standards　for　Fe,　Mn　and　ammonia　under　designing　filtration　rate.　Fe,　Mn,　and　ammonia　was　mainly　removed　at　0.2　m,　1.2　m,　and　1.0　m　in　steady　phase,　respectively.　Both　nitrification　and　ANAMMOX　contributed　to　nitrogen　conversion.　The　calculation　results　demonstrated　that　autotrophic　nitrogen　removal　proportion　was　about　48.3%　in　the　steady　operation　period.　Meanwhile,　11　putative　Mn　oxidizing　bacteria　(MnOB)　were　detected　and　putative　MnOB　was　dominant　in　all　the　samples;　Candidatus　Kuenenia　was　the　only　detected　Anaerobic　Ammonium　Oxidation　(ANAMMOX)　genus.　The　relationship　between　removal　efficiency　along　the　height　and　the　taxonomic　results　was　also　concluded.