In　this　study,　the　caching　bed　reactor,　which　was　using　hydrophilic　material　of　acrylic　resin　fiber　(ARF)　as　carrier　material,　was　used　to　treat　domestic　wastewater.　The　effect　of　three　different　DO　concentrations　on　the　removal　of　COD,　NH4+-N　and　TN　were　investigated　under　the　conditions　of　hydraulic　retention　time　(HRT)　=　8h　and　sludge　reflux　rate　of　100%.　The　average　removal　efficiency　of　COD　reached　at　86.4%,　87.5%　and　87.3%　respectively.　The　average　NH4+-N　removal　rate　increased　with　the　DO　concentration　increasing,　which　reached　at　89.21%,　92.02%　and　99.31%.　When　DO=2.0　similar　to　3.0　mg/L,　the　best　TN　removal　rate　of　36.35%　was　obtained.　Meanwhile,　FISH　analysis　indicated　that　the　higher　DO　concentration,　the　greater　number　of　nitrifying　bacteria.