Domestic　wastewater　was　treated　by　using　three　parallel　sequencing　batch　reactors　(SBR)　at　the　pH　of　7.9-8.0　to　optimize　aeration　duration　of　partial　nitrification.　The　partial　nitrification　was　achieved　and　maintained　by　controlling　the　aeration　time　of　t/2,　t/4,　t/8　respectively　(t　was　aeration　time)　before　appearance　of　＇ammonia　valley＇.　Nitrite　accumulation　ratios　were　improved　by　50%,　65%,　90%　respectively　in　the　three　reactors　which　were　operated　in　145　days.　FISH　quantitative　analysis　showed　that　the　percentage　of　ammonia　oxidizing　bacteria　(AOB)　in　the　reactors　increased　differently.　AOB　and　nitrite　oxidizing　bacteria　(NOB)　was　3.89%　and　0.27%　of　the　total　bacteria　respectively　in　No.3　reactor,　which　showed　that　AOB　is　the　dominant　bacteria　in　nitrifying　bacteria.　It　is　concluded　that　synergistic　effect　between　the　optimal　control　of　aeration　duration　and　the　inhibition　of　FA　would　be　the　key　factors　to　rapid　start-up　and　maintain　the　stable　nitrification.