A　system　that　combines　an　ion　exchange　membrane　and　ultrafiltration　membrane　(IEM-UF)　to　form　a　simultaneous　separation　and　denitrification　system　was　proposed　for　domestic　sewage　with　a　low　carbon/nitrogen　ratio.　The　removal　of　nitrogen　and　COD　in　the　system　was　studied　under　a　three　phase　operating　condition.　The　characteristics　of　the　microbial　community　in　each　reactor　were　analyzed　using　metagenomics.　The　results　show　that,　the　average　rate　of　ammonia　nitrogen　enrichment　in　the　separator　reached　above　116.1%　when　the　current　intensity　was　0.2　A.　When　the　system　was　at　C/N　2.80　and　operating　well,　the　average　removal　rates　of　COD　and　TN　reached　above　90%　and　50%,　respectively.　The　maximum　removal　rate　of　TN　was　above　65.4%.　The　results　of　metagenomics　showed　a　genus　of　phylum　Nitrospirae　(Nitrospira)　and　a　genus　of　phylum　Proteobacteria　(Nitrosomonas),　with　the　proportions　of　12.23%　and　2.31%,　respectively.　In　the　denitrifying　reactor,　Dechloromonas,　Thauera,　and　Azospira　were　detected　in　the　proportions　4.57%,　1.76%,　and　1.03%,　respectively.　These　proportions　were　far　larger　than　those　of　other　bacteria　in　this　reactor.　Meanwhile,　the　presence　of　iron　autotrophic　denitrifying　bacteria　increased　the　denitrification　efficiency　of　the　system.　©　2019,　Science　Press.　All　right　reserved.