Rare　earth　element　tailings　(REEs)　wastewater,　which　has　the　characteristics　of　high　ammonia　nitrogen　(NH4+-N)　and　low　COD.　It　can　cause　eutrophication　and　biotoxicity　in　water　which　is　produced　in　high　volumes,　requiring　treatment　before　final　disposal.　Microalgae-Bacteria　symbiotic　(MBS)　system　can　be　applied　in　REEs　wastewater,　but　its　low　extent　of　nitrogen　removal　and　instability　limit　its　application.　By　adding　biodegradable　carrier　as　both　carbon　source　and　carrier,　the　system　can　be　stabilized　and　the　efficiency　can　be　improved.　In　this　work,　the　extent　of　NH4+-N　removal　reached　100%　within　24　h　in　a　MBS　system　after　adding　loofah　under　optimal　con-ditions,　and　the　removal　rate　reached　127.6　mg　NH4+-N　center　dot　L-　1　center　dot　d-　1.　In　addition,　the　carbon　release　from　loofah　in　3　d　reached　408.7　mg/L,　which　could　be　used　as　a　carbon　source　to　support　denitrification.　During　90　d　of　operation　of　the　MBS　system　loaded　with　loofah,　the　effluent　NH4+-N　was　less　than　15　mg/L.　At　phylum　level,　Proteobacteria　were　dominant　which　accounted　for　78.2%.　Functional　gene　analysis　showed　that　enhancement　of　microalgae　assimilation　was　the　main　factor　affecting　NH4+-N　removal.　This　work　expands　our　understanding　of　the　enhanced　role　of　carbon-based　carriers　in　the　denitrification　of　REEs　wastewater.