Four　mini　experiments　were　conducted　at　different　conditions.　The　heterotrophic　microorganisms　on　the　aerobic　granular　sludge　surface　consumed　organic　compounds　at　the　initial　stage　of　aeration.　The　denitrification　rate　and　the　efficiency　of　NO2--N　and　NO3--N　removal　were　relatively　low.　Therefore,　under　the　normal　temperature　conditions　(20-23),　aerobic　granular　sludge　sequencing　batch　reactor　(SBR)　was　operated　in　the　two-stage　aeration　mode(first　in　low　aeration　then　in　high　aeration　mode).　The　low　aeration　time　were　carried　out　at　1,　2　and　3　hours　stages　respectively,　and　the　characteristics　of　the　granular　sludge　and　its　effects　on　microorganisms　were　analyzed　by　scanning　electron　microscopy　(SEM)　and　fluorescence　in　situ　hybridization　(FISH)　technique.　The　results　show　that　the　increase　in　the　aerobic　granular　sludge　(AGS)　particle　size　improved　the　denitrification　capacity;　the　denitrification　rate　of　NO2--N　was　the　highest　at　low　aeration　mode　with　2　h　and　reached　9.66　mg·(g·h)-1.　The　accumulation　rate　of　nitrite　increased　to　77.84%　and　the　total　nitrogen　removal　rate　to　70%.　The　bacterial　count　inside　the　granular　sludge　increased　and　they　were　mainly　cocci,　bacillus,　and　ellipsoidal　bacteria.　Moreover,　the　proportion　of　ammonia-oxidizing　bacteria　in　total　bacterial　count　increased　from　13.70%　to　15.40%.　Therefore,　the　two-stage　aeration　process　achieved　shortened　simultaneous　nitrification　and　denitrification　processes　and　showed　a　good　denitrification　performance.　©　2017,　Science　Press.　All　right　reserved.