In　order　to　reveal　the　succession　of　microbial　community　diversity　in　a　hybrid　membrane　bioreactor　(MBR)　and　provide　microbial　evidence　for　technique　improvements,　total　microbial　DNA　is　extracted　from　six　samples　which　are　collected　three　times　respectively　from　mixed　liquor　and　biofilm　of　a　MBR,　16SrDNA　fragments　were　amplified　from　the　total　DNA　successfully　using　a　pair　of　universal　bacterial　16SrDNA　primer,　GC968F　and　1492R,　and　then　the　amplified　PCR　are　used　for　denaturing　gradient　gel　electrophoresis　(DGGE)　analysis.　DGGE　analysis　indicated　that　a　noticeable　change　takes　place　in　microbial　structure　at　initial　stages　of　MBR　operation.　In　the　whole　operation,　bacterial　community　structures　are　higher.　In　this　bioreactor,　because　of　the　existence　of　filling,　there　might　be　two　different　modes　of　denitrification　in　the　reactor　because　there　might　be　anaerobic　environment　in　it.　Two　months　later,　some　increasing　bacteria　has　greater　impact　on　the　production　and　accumulation　of　membrane　pollutants.