The　removal　mechanism　of　ammonia　nitrogen　(NH4+-N)　was　analyzed　about　＇two-stage　aeration　and　two-stage　filtration＇　process　that　was　used　to　remove　high　iron　(Fe2+＞8.0mg/L),　manganese　(Mn2+＞3.0mg/L)　and　NH4+-N　(＞3.0mg/L)　from　low　temperature　(5~7.8)　groundwater　in　a　drinkingwater　plant.　The　experiments　showed　that　there　was　45.22%　and　35.97%　nitrogen　losses　(TNloss)　in　the　primary　and　secondary　filter　columns,　respectively,　and　the　actual　DO　consumption　was　24.67%　and　22.27%　lower　than　the　theoretical　DO　consumption.　Moreover,　the　TNloss　process　was　proved　to　be　accompanied　with　DO　consumption　by　DO　measurement　relationship.　There　was　a　good　linear　relationship　between　TNloss　and　its　DO　consumption,　R2＞0.970.　The　analysis　demonstrated　that　autotrophic　nitrogen　removal　(N-removal)　was　the　cause　of　TNloss,　which　was　independent　on　the　adsorption,　biological　assimilation,　heterotrophic　denitrification　and　manganese　oxidative　coupling　denitrification.　The　calculation　based　on　quantitative　relationship　between　nitrogen　conservation　and　DO　measurement　indicated　that　the　contribution　of　autotrophic　N-removal　to　NH4+-N　removal　was　51.40%　and　40.93%　in　the　primary　and　secondary　filter　columns,　respectively.　Both　the　nitrification　reaction　and　the　autotrophic　N-removal　process　were　the　significant　removal　mechanism　of　NH4+-N.　Moreover,　with　the　higher　concentration　of　NH4+-N,　the　contribution　of　autotrophic　N-removal　was　also　higher.　©　2017,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.