In　this　study,　nitrite　accumulation　was　investigated　under　different　DO　conditions　and　different　hydroxylamine　addition　methods　during　the　domestic　wastewater　treatment.　Two　sequencing　batch　reactors　in　parallel　were　operated　under　cyclic　aerobic　and　anoxic　conditions　with　the　DO　concentration　of　2.0　and　4.0　mg/L　in　aerobic　phase.　The　nitrite　accumulation　rate　during　high　DO　conditions　increased　to　44.8　and　66.7%　in　20　days.　During　hydroxylamine　addition,　the　NAR　increased　over　90%　under　the　continuous　and　intermittent　hydroxylamine　addition.　Continuous　hydroxylamine　addition　could　result　in　a　more　efficient　and　rapid　nitrite　accumulation.　The　findings　suggested　that　comammox　could　be　the　main　reason　for　the　failure　of　partial　nitrification　in　a　low　DO　environment　(　＜　0.5　mg/L).　The　nitrogen　variation　during　typical　cycles　showed　that　the　continuous　hydroxylamine　addition　suppressed　the　activity　of　NOB　and　the　ammonia　oxidation　rate.　Further,　the　qPCR　results　indicated　that　the　abundance　of　comammox　amoA　(ranged　from　6.25　x　10(7)　to　4.16　x　10(8)　copies/g　VSS)　was　higher　than　those　of　AOB　amoA　and　Nitrobacter　in　sludge　samples.　The　findings　from　the　current　study　may　enrich　our　understanding　of　partial　nitrification　and　its　control　strategy.