Microalgae-bacteria　symbiosis　system　(MBS)　appear　to　be　a　promising　way　for　treating　the　rare　earth　elements　(REEs)　wastewater　due　to　the　natural　symbiotic　interactions　between　microalgae　and　bacteria.　Herein,　we　investigated　the　effect　of　different　inoculation　ratios　of　microalgae　and　bacteria　including　3:1　(MB_1),　1:1　(MB_2)　and　1:3　(MB_3)　on　NH4+-N　removal　from　REEs　wastewater　and　analyzed　the　corresponding　biological　mechanism.　The　NH4+-N　removal　rate　with　MB_3　reached　17.69　+/-　0.45　mg　NH4+-N/L　d-1,　which　was　2.58　times　higher　than　that　in　single　microalgae　system.　The　results　were　further　verified　in　continuous　feeding　photobioreactors　and　kept　stable　for　100　days.　Metagenomic　analysis　revealed　that　the　abundance　of　genes　related　to　microalgae　assimilation　increased　by　14　%-50　%　in　answer　to　photosynthesis　and　NH4+-N　absorption,　while　that　related　to　nitrification　apparently　dropped,　indicating　that　MBS　was　a　sustainable　method　capable　of　enhancing　NH4+-N　removal　from　REEs　wastewater.