Microalgae　appear　to　be　a　promising　and　ecologically　safe　way　for　nutrients　removal　from　rare　earth　tailings　(REEs)　wastewater　with　CO2　fixation　and　added　benefits　of　resource　recovery　and　recycling.　In　this　study,　a　pilot　scale　(50　L)　co-flocculating　microalgae　photobioreactor　(Ma-PBR)　as　constructed　and　operated　for　140　days　to　treat　REEs　wastewater　with　low　C/N　ratio　of　0.51-0.56.　The　removal　rate　of　ammonia　nitrogen　(NH4+-N)　reached　88.04%　and　the　effluent　residual　concentration　was　as　low　as　9.91　mg/L　that　have　met　the　Emission　Standards　of　Pollutants　from　Rare　Earths　Industry　(GB　26451-2011).　Timely　supplementation　of　trace　elements　was　necessary　to　maintain　the　activity　of　microalgae　and　then　prolonged　the　operation　time.　The　dominant　phyla　in　co　-flocculating　microalgae　was　Chlorophyta,　the　relative　abundance　of　which　was　higher　than　80%.　Tetradesmus　belonging　to　Chlorophyceae　was　the　dominant　genus　with　relative　abundance　of　80.35%.　The　results　provided　a　practical　support　for　the　scaling-up　of　Ma-PBR　to　treat　REEs　wastewater.