In　this　study,　the　start　of　partial　nitrification　(activated　sludge)-anaerobic　ammonia　oxidation　(immobilized　fillers)-denitrification　(immobilized　fillers)　and　stable　nitrogen　removal　in　the　treatment　of　rare　earth　element　tailings　wastewater　were　explored.　The　results　showed　that,　at　25-30　°C,　partial　nitrification　could　be　rapidly　established　by　controlling　the　combination　of　average　free　ammonia　concentration　(25.4-60.2　mg/L)　and　dissolved　oxygen　concentration　(0.5　mg/L).　Adopting　the　stepwise　substrate　(three　stages)　and　shortening　hydraulic　retention　time　(HRT)　methods,　the　total　nitrogen　removal　rate　of　anaerobic　ammonia　oxidation　(anammox)　immobilized　fillers　reached　up　to　0.99　kg　N•(m3•d)-1.　Adopting　the　C/N　ratio　of　4.5:1　and　shorter　HRT　methods,　the　total　nitrogen　removal　rate　of　denitrification　immobilized　fillers　reached　up　to　1.07　kg　N•(m3•d)-1.　The　activities　of　the　anammox　and　denitrification　immobilized　fillers　were　increased　by　8.39　and　4.46　times,　respectively.　At　steady　state　operation,　the　average　effluent　ammonia　nitrogen　concentration　was　3.01　mg/L,　with　an　average　effluent　total　nitrogen　concentration　of　5.11　mg/L,　which　met　the　requirements　of　the　＇Emission　Standard　for　Pollutants　from　Rare　Earth　Industry＇GB　26451-2011.　High-throughput　sequencing　technology　showed　that　the　relative　abundance　ratios　of　Nitrosomonas　and　Nitrospira　changed　from　0.36:1-108.05:1.　The　dominant　bacterial　genera　of　the　anammox　immobilized　fillers　was　Candidatus　Kuenenia,　and　that　of　denitrification　immobilized　fillers　were　Pseudomonas　and　Thauera.　This　process　provides　a　new　technical　approach　for　rare　earth　element　tailings　wastewater　treatment,　with　high　significance　in　engineering.　©　2022　Elsevier　Ltd.