In　a　simultaneous　nitrogen　and　phosphorus　removal　system,　both　white　and　yellow　aerobic　granular　sludge　(WG　and　YG)　appeared.　Scanning　electron　microscopy　(SEM)　was　used　to　observe　the　micro-morphology　of　WG　and　YG.　Illumina　HiSeq　2500　platform　was　applied　to　investigate　their　bacterial　and　fungal　communities,　and　to　explore　the　reasons　for　the　formation　of　WG.　WG　was　loose　and　irregular,　while　YG　was　compact　and　regular.　The　results　of　SEM　indicated　that　bacillus　and　coccus　were　dominant　on　the　surface　of　WG　and　YG,　respectively.　The　bacterial　community　of　WG　and　YG　was　similar,　while　their　fungal　community　was　significantly　different.　The　α-diversity　of　WG　was　higher　than　that　of　YG.　Proteobacteria　and　Bacteroidetes　were　the　dominant　phyla　in　WG　and　YG.　Their　relative　abundances　in　WG　were　68.85%　and　26.61%,　respectively.　For　YG,　their　relative　abundances　were　82.52%　and　12.30%,　respectively.　Candidatus　competibacter(22.13%),　Candidatus　accumulibacter　(8.95%)　and　Chiayiivirga　(7.37%)　dominated　in　WG.　Candidatus　competibacter(47.94%),　Chiayiivirga　(6.95%)　and　Xanthomonas　(7.06%)　were　the　dominant　genera　in　YG.　Ascomycota　and　Rozellomycota　were　the　main　fungal　phyla　in　WG　and　YG,　with　relative　abundances　of　50.10%　and　81.77%,　respectively.　Penicillium　and　Candida　were　the　dominant　filamentous　fungi　in　WG.　When　YG　disintegrated　into　small　zoogloea,　it　attached　to　the　framework　of　filamentous　fungi　and　grew　rapidly,　which　might　be　a　reason　for　the　formation　of　WG.　The　low　relative　abundance　of　Candidatus　competibacter　might　be　a　reason　for　the　loose　shape　of　WG.　©　2017,　Editorial　Board,　Research　of　Environmental　Sciences.　All　right　reserved.