Aiming　at　the　water　quality　of　complex　composition　and　low　chemical　oxygen　demand　(COD)　in　rare　earth　tailings　wastewater,　the　anammox　immobilized　fillers　were　used　for　treatment.　First,　the　adaptation　and　domestication　of　the　anammox　immobilized　fillers　were　carried　out,　and　then　the　nitrogen　removal　performance　of　the　anammox　immobilized　fillers　alone　and　the　anammox　immobilized　fillers　coupled　with　denitrification　immobilized　fillers　in　the　treatment　of　rare　earth　tailings　wastewater　were　respectively　explored.　The　results　showed　that,　the　anammox　immobilized　fillers　had　good　adaptability　to　rare　earth　tailings　wastewater.　After　the　adaptation　and　domestication　by　adopting　the　stepped　substrate　and　shortening　hydraulic　retention　time　(HRT)　operation　strategy,　the　total　nitrogen　removal　load　rate　(NRR)　of　the　anammox　immobilized　fillers　could　reach　up　to　0.99kg　N/(m3·d),　which　was　8.39　times　higher　than　that　before　adaptation　and　domestication.　The　results　of　high-throughput　sequencing　showed　that　the　relative　abundance　of　the　anammox　dominant　genus　(Candidatus　Kuenenia)　increased　from　5.53%　to　35.67%,　which　achieved　effective　enrichment,　while　the　dominant　genus　(Candidatus　Brocadia)　before　adaptation　and　domestication　were　not　adapted　to　the　environment　and　were　eliminated.　When　the　concentration　of　ammonia　nitrogen　in　the　raw　water　fluctuated,　the　NRR　of　the　anammox　immobilized　fillers　alone　for　treating　rare　earth　tailings　wastewater　could　reach　up　to　1.02kg　N/(m3·d),　the　average　concentration　of　effluent　ammonia　nitrogen　was　3.98mg/L,　the　removal　rate　of　ammonia　nitrogen　and　nitrite　nitrogen　reached　94.43%,　and　60%　of　organic　carbon　sources　were　saved.　By　controlling　the　C/N　ratio　to　1.5∶1,　the　coupling　of　the　anammox　and　denitrification　immobilized　fillers　was　successfully　achieved,　and　the　activity　of　the　anammox　immobilized　fillers　was　not　significantly　affected.　The　average　concentration　of　total　nitrogen　in　the　effluent　was　0.65mg/L,　the　average　removal　rate　of　total　nitrogen　was　95.6%,　and　84%　of　organic　carbon　sources　were　saved　theoretically.　©　2023　Chemical　Industry　Press.　All　rights　reserved.