To　investigate　the　influence　of　DO　concentration　on　the　characteristics　of　catching　bed　reactor,　the　removal　efficiency　of　COD,　NH4+-N　and　TN　were　analyzed　under　the　DO　concentrations　at　1.0~2.0　mg/L,　2.0~3.0　mg/L　and　3.0~4.0　mg/L,　respectively.　Meanwhile,　ammonia-oxidizing　bacteria　(AOB)　community　and　diversity　in　each　reactor　were　examined　using　restricted　fragment　length　polymorphism　(RFLP),　and　sequencing　of　amoA　genes.　The　results　showed　that　higher　COD　and　NH4+-N　removal　efficiency　were　received　under　different　DO　concentrations,　NH4+-N　removal　efficiency　increased　with　the　DO　concentration　increase.　The　diversity　of　AOB　was　abundant　in　different　DO　concentrations,　but　the　communities　and　species　of　AOB　were　effect　greatly　by　DO　concentration.