The　sludge　that　deriving　from　a　stable　CANON　biofilter　was　seeded　to　two　same　SBR　reactors　at　room　temperature　(22~26°C),　in　which　the　influence　of　DO　on　the　nitrogen　removal,　stability　and　sludge　morphology　of　CANON　process　were　studied　by　setting　different　initial　DO　and　DO　gradient.　The　results　showed　that　the　reactor　with　the　initial　DO　of　0.05~0.1　mg/L　could　run　stably　with　the　ammonia　and　TN　removal　efficiency　of　99%　and　85.4%,　respectively,　while　the　reactor　with　initial　DO　of　(0.40±0.5)　mg/L　showed　rather　lower　removal　efficiencies　of　99%　and　0,　respectively.　DO　concentration　was　increased　gradually　from　0　to　0.2,　0.4,　0.5　mg/L,　correspondingly,　the　anaerobic　ammonia　removal　rate　reached　to　35.95,　23.89,　31.50,　19.25　mgN/(L·h),　respectively.　Moreover,　the　reactor　could　still　run　normally　after　two　hours＇　extended　aeration　The　activity　of　the　CANON　reactor　went　up　with　the　increase　of　DO　within　a　certain　DO　range,　and　the　higher　DO　presented　a　large　and　irreversible　impact　on　the　early　vaccinating　CANON　reactor　while　showed　little　and　reversible　influence　on　the　stable　CANON　reactor.　Micrographs　indicated　the　tendency　of　sludge　granulation　in　the　stable　CANON　reactor.