Efficient　nitrogen　removal　from　domestic　sewage　was　obtained　in　a　sequencing　batch　biofilm　reactor　(SBBR)　operated　in　alternate　anaerobic/oxic/anoxic　(A/O/A)　mode.　For　the　influent　total　nitrogen　(TN)　ranging　from　30.0　to　63.3　mg　N.L-1,　the　average　nitrogen　removal　efficiency　was　90.3　+/-　2.9%　with　removal　rate　of　42.3-76.2　mg　N.L-1.d(-1).　According　to　the　high-throughput　sequencing　analysis,　anammox　bacteria　(0.40-0.61%)　were　enriched,　and　some　genera　that　could　carry　out　endogenous　denitrification,　including　Comamonadaceae　and　Dechloromonas,　were　observed,　indicating　that　the　special　conditions　in　the　SBBR　might　combine　autotrophs　with　heterotrophs　for　enhanced　nitrogen　removal.　The　nitrogen　removal　mechanism　was　analyzed　based　on　stoichiometry　and　continuous　and　cyclic　tests.　Results　indicate　that　partial　nitrification-anammox　was　the　primary　nitrogen　removal　pathway,　accounting　for　60.4%　of　the　TN　removed.　Endogenous　denitrification　accounted　for　25.7%　of　the　TN　removed.　Overall,　the　A/O/A　mode　could　combine　autotrophic　nitrogen　removal　with　endogenous　denitrification,　enhancing　sewage　nitrogen　removal.