In　this　study,　a　CEM-UF　composite　membrane　with　ammonia　nitrogen　enrichment　and　separation　characteristics　was　combined　with　nitrification/denitrification　to　treat　low　C/N　wastewater.　The　denitrification　characteristics　of　low　C/N　wastewater　at　different　flow　ratios　were　investigated,　and　the　structural　characteristics　of　functional　microbial　communities　in　nitrifying　and　denitrifying　activated　sludge　were　analyzed　by　16Sr　DNA　high-throughput　sequencing.　The　results　showed　that　influent　TN　was　60　mg•L-1,　COD/TN　was　2.65,　the　nitrification　effect　of　each　flow　rate　was　good,　and　the　average　ammonia　nitrogen　removal　rate　was　98.7%.　When　the　flow　ratio　increased　from　1:2　to　1:6,　the　m(COD)/m(NO3--N)　of　denitrification　was　increased,　and　the　removal　of　average　nitrate　nitrogen　reached　its　highest　level　at　1:6,　which　was　86.28%,　and　the　removal　of　total　nitrogen　increased　from　22.56%　to　46.8%.　An　analysis　of　Illumina　sequencing　showed　that　nitrogen　fixing　bacteria　Proteobacteria　accounted　for　30.9%,　and　the　important　nitrite　oxidizing　bacteria,　Nitrospirae,　accounted　for　3.06%.　At　the　genus　level,　Nitrosomonas　and　Nitrosospira,　belonging　to　the　ammonia　oxidizing　bacteria　(AOB)　category　and　Nitrospira　and　Nitrobacter,　belonging　to　the　nitrite　oxidizing　bacteria　(NOB)　category　were　detected.　The　ratio　of　AOB　and　NOB　bacteria　was　high,　which　is　consistent　with　good　nitrification　in　the　nitrification　reactor.　The　dominant　bacteria　in　denitrification　sludge　were　Proteobacteria　(53.13%),　followed　by　Bacteroidetes　(10.93%).　A　variety　of　bacteria　related　to　denitrification　were　detected　at　the　genus　level,　such　as　Dechloromonas,　Thauera,　Castellaniella,　Alicycliphilus,　Azospira,　Comamonas,　Caldilinea,　and　Saccharibacteria.　The　proportion　of　denitrifying　bacteria　was　25.91%　as　denitrifying　bacteria　microbial　species　were　rich　in　the　denitrifying　sludge,　giving　a　good　denitrification　effect.　©　2018,　Science　Press.　All　right　reserved.