A　SBR　inoculated　with　conventional　activated　sludge　was　employed　to　cultivate　aerobic　granular　sludge.　Under　the　selective　pressure　of　settling　time,　the　formation　of　nitrifying　granules　enriched　with　the　ammonia　oxidizing　bacteria　(AOB)　was　achieved　by　increasing　the　nitrogen　loading　rate　(NLR).　The　nitrifying　granule　was　shaped　like　a　sphere　or　an　ellipsoid　with　an　equivalent　diameter　of　approximate　1.1　mm,　an　average　settling　velocity　of　1.9　cm·s-1　and　the　sludge　volume　index　of　18.2~31.4　mL·　g-1.　As　the　aerobic　granular　system　was　operated　stably,　the　NLR　reached　a　value　of　0.0455　kgNH4+-N·(kg　MLSS·d)-1　with　ammonia　removal　efficiency　above　95%　and　nitrite　accumulation　ratio　in　the　range　of　80%~90%.　The　NLR　was　4.55　times　higher　than　that　of　the　start-up　period.　The　enrichment　of　the　nitrifying　bacteria　was　quantified　by　FISH　analysis　which　indicated　that　AOB　was　14.9%　of　the　total　bacteria　and　nitrite　oxidizing　bacteria　(NOB)　was　0.89%.　It　is　concluded　that　the　associated　inhibition　of　FA　at　the　start　of　the　reaction　and　FNA　at　the　end　of　the　reaction　would　be　the　key　factors　to　start　up　and　maintain　the　stable　nitritation.