Aerobic　granular　sludge　(AGS)　was　cultivated　in　a　sequencing　batch　reactor　(SBR).　In　this　study,　AGS　was　broken　during　the　formation　process　and　then　mature　AGS　formed　again.　The　microbial　community　dynamics　during　two　sludge　granulation　processes　were　investigated　using　high-throughput　sequencing　to　reveal　the　dominant　bacteria　beneficial　to　AGS　formation.　The　abundance　dynamics　of　nitrifying　microorganisms　were　analyzed　by　a　quantitative　polymerase　chain　reaction　(qPCR).　The　results　showed　that　the　amount　of　extracellular　protein　and　polysaccharides　increased　during　two　sludge　granulation　processes.　The　abundance　of　ammonia　oxidizing　archaea　(AOA)　increased　during　the　first　AGS　formation　process　and　during　the　process　of　AGS　maturation.　The　abundance　of　ammonia　oxidizing　bacteria　(AOB)　decreased　during　the　first　AGS　formation　process,　while　it　maintained　a　higher　abundance　than　AOA　during　AGS　cultivation.　Microbial　diversity　decreased　with　AGS　formation.　The　relative　abundance　of　Proteobacteria　increased　by　12.29%　and　5.90%　during　two　sludge　granulation　processes,　respectively.　Candidatus　Competibacter　belonging　to　Proteobacteria　was　enriched　during　two　sludge　granulation　processes,　accounting　for　14.20%　in　mature　AGS.　Overall,　extracellular　protein　and　polysaccharides　may　have　contributed　to　the　sludge　granulation.　Both　AOA　and　AOB　might　have　been　involved　in　ammonia　oxidation.　This　study　indicated　that　Ca.　Competibacter　might　contribute　to　AGS　formation.　©　2018,　Science　Press.　All　right　reserved.