The　present　study　sought　to　treat　the　ion-adsorption　type　rare　earth　mine　wastewater　in　a　pilot　plant　system　using　the　nitritation-denitrification　process　with　immobilized　biological　fillers.　Meanwhile,　the　microbial　community　structure　in　the　immobilized　fillers　was　analyzed.　The　ammonia　nitrogen　removal　rate　of　the　nitritation　fillers　reached　0.43　kg　N　m(-3)　d(-1)　on　day　61　(28.1　degrees　C)　and　the　total　nitrogen　removal　rate　of　the　denitrification　fillers　reached　0.51　kg　N　m(-3)　d(-1)　on　day　58　(27.8　degrees　C)　under　the　hydraulic　retention　time　of　3.4　hr　and　a　fillers　volume　ratio　of　8%　(v/v).　The　average　NH4+-N　and　TN　removal　efficiencies　of　the　nitritation-denitrification　process　were　96.9%　and　96.8%,　respectively,　during　the　steady　state　operation　period　(day　26-72).　The　results　also　indicate　that　high　DO　(5.5-6.5　mg　L-1)　could　induce　rapid　growth　of　nitrite-oxidizing　bacteria　(NOB)　in　the　nitritation　fillers,　even　though　the　initial　NOB　proportion　is　extremely　low.　The　optimal　operational　performance　of　the　denitrification　fillers　reactor　was　the　COD/(NO2--N　+　NO3--N)　ratio　of　3.7-4.2.　The　high-throughput　sequencing　analysis　showed　that　the　functional　bacteria　in　the　immobilized　fillers　could　maintain　a　competitive　advantage.　The　abundance　of　Nitrosomonas　in　the　nitritation　fillers　increased　from　6.58%　to　21.24%,　while　Thauera　and　Ottowia　were　the　dominant　denitrifying　bacteria　genera　in　the　denitrification　fillers.