The　nitritation　in　side-line　treatment　system　was　proposed　considering　the　ammonium　oxidizing　bacteria　(AOB)　content　was　high,　and　nitrite　oxidizing　bacteria　(NOB)　content　was　low.　The　excess　sludge　discharged　from　above　system　was　introduced　to　the　domestic　wastewater　treatment　system　so　as　to　achieve　stable　nitritation　via　this　bioaugmentation.　The　results　show　that　stable　nitritation　is　achieved　in　side-line　treatment　system　by　using　the　inhibition　of　free　ammonia　(FA)　and　free　nitrous　acid　(FNA)　on　the　anabolism　of　NOB,　and　the　nitrite　accumulation　rate　(RNA)　is　97%　in　average.　Nitritation　can　be　quickly　start-up　in　mainstream　treatment　system　by　adding　nitritation　sludge　and　controlling　dissolved　oxygen　(DO).　It　could　be　reconstructed　with　a　nitrite　accumulation　rate　(RNA)　from　1%　to　89%　within　15　d　when　the　mass　concentration　of　DO　is　0.96　mg/L　and　nitritation　adding　rate　is　5.6%.　Achieving　stable　nitritation　in　domestic　wastewater　treatment　based　on　bioaugmentation　gives　a　possible　solution　to　achieve　nitrogen　removal　from　domestic　wastewater　via　anammox.　©　2016,　Central　South　University　Press.　All　right　reserved.