To　further　investigate　the　effect　of　dissolved　oxygen　(DO)　on　microbial　community　of　nitrify　bacteria　in　the　activated　sludge,　the　microbial　community　of　enriched　nitrify　sludge　under　the　different　DO　level　was　analyzed　by　high-throughput　sequencing　technology.　Results　show　that　for　nitrify　sludge　including　both　ammonium　oxidizing　bacteria　(AOB)　and　nitrite　oxidizing　bacteria　(NOB),　low-DO　condition　increase　the　microbial　diversity,　and　high-DO　enriches　the　nitrifying　functional　bacteria　(Nitrosomonas,　Nitrospira).　For　nitrify　sludge　only　including　NOB,　there　is　no　obvious　difference　of　microbial　diversity　between　low-DO　condition　and　high-DO　condition,　and　Nitrospira　prefers　to　grow　under　the　low-DO　condition.　Moreover,　different　DO　conditions　also　affect　the　microbial　community　of　other　bacteria　except　nitrifyer.　©　2017,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.