In　order　to　find　the　better　method　to　deal　with　late　landfill　leachate,　the　stable　partial　nitrification　system　was　operated　in　the　MBR　(membrane　bioreactor).　The　microbial　community　structure　of　the　stable　partial　nitrification　phase　was　investigated　by　the　total　bacterial　clone　library　and　the　cloning　library　of　ammonia　oxidizing　bacteria　(AOB)　functional　gene　amoA.　82　positive　clones　were　selected　randomly　from　16S　rDNA　clone　library　and　their　sequence　was　determined.　The　results　show　that　there　are　four　dominant　bacterium　groups　in　the　stable　partial　nitrification　phase:　Proteobacteria　(64.65%),　uncultured　bacterium　(18.3%),　Bacteroidetes　(9.76%),　and　Firmicutes　(7.32%).　Building　on　the　cloning　library　of　AOB＇s　functional　gene　amoA,　73　positive　clones　were　selected　from　the　library　and　their　sequence　was　also　determined.　Compared　with　basic　local　alignment　search　tool(BLAST),　the　results　show　that　only　the　Nitrosomonas　and　Uncultured　bacterium　are　detected　in　the　system,　and　their　proportion　is　41.1%　and　58.9%,　respectively.　This　phenomenon　show　that　the　number　of　Nitrosomonas　is　maximum　in　this　system.　At　the　same　time,　the　existence　of　many　unknown　bacterial　species　showed　that　there　are　a　large　number　of　microbial　resources　in　the　system　and　needing　further　development.　©　2017,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.