In　this　study,　a　membrane　aerated　biofilm　reactor　(MABR)　coupled　partial　nitritation/anammox　(PN/A)　system　was　established　for　high-rate　nitrogen　removal.　Results　showed　that　the　nitrogen　removal　efficiency　of　90.34%　was　finally　obtained　when　influent　ammonia　increased　from　150　mg　L-1　to　300　mg　L-1.　Based　on　the　fluorescence　spectroscopy　technology,　the　raised　hydrophobicity　tryptophan　in　extracellular　polymeric　substances　(EPS)　promoted　biofilm　formation　and　bacteria　aggregation.　16S　rRNA　gene　amplicon　sequencing　revealed　that　the　relative　abundance　of　AOB　and　AnAOB　was　also　enhanced　by　ammonia　(Nitrosomonas　and　Candidatus　Brocadia　increased　by　6.02　%　and　10.06　%　in　biofilm,　respectively),　which　further　facilitated　nitrogen　removal　efficiency.　Furthermore,　the　key　functional　genes　involved　in　partial　nitritation　and　anammox,　especially　hao　and　nirK,　up-regulated　by　1.31　and　1.26　times,　respectively,　accelerating　the　electron　generation　and　consumption.　Therefore,　raising　influent　ammonia　content　intensified　microbial　electron　transfer　behavior　and　high-rate　nitrogen　metabolism.