This　study　achieved　stable　nitritation　by　eliminating　both　Nitrobacter　and　Nitrospira　through　combing　nitrite　exposure　inhibition　with　high　dissolved　oxygen　(DO)　reactivation.　After　treated　by　nitrite　exposure　(5-30　mg.L-1),　nitrite-oxidizing　bacteria　(NOB)　of　two　nitrifying　reactors　(RL　and　RH)　was　suppressed　seriously　than　ammonium-oxidizing　bacteria　(AOB)　with　faster　activity　decay　rate　(0.035　+/-　0.003　d(-1))　and　larger　population　reduction　as　well　as　slower　functional　gene　transcription,　wherein　Nitrobacter　was　inhibited　more　significantly　than　Nitrospira.　During　reactivation　period,　the　R-H　(high　DO:　2.5-3.0　mg.L-1)　achieved　nitritation　with　high　NAR　of　97.9%,　which　was　twice　faster　than　R-L　(low　DO:　0.1-0.6　mg.L-1).　Though　temperature　declined　to　16.6　degrees　C,　R-H　remained　constant　nitritation　with　ideal　effluent　NO2--N:NH4+-N　of　1:1　for　anammox.　Further　analysis　indicated　that　high　DO　reactivation　accelerated　AOB　overcome　NOB　by　promoting　AOB　growth　but　severely　inhibited　Nitrospira.　The　findings　provided　novel　insights　into　suppressing　NOB　in　targeted　ways　which　facilitated　mainstream　deammonifcation.