The　aim　of　the　present　study　was　to　investigate　the　effect　of　alkaline　sludge　fermentation　products　as　a　carbon　source　on　the　nitrification　process　and　performance.　During　the　operation　of　a　biological　nitrogen　removal　(BNR)　system　with　sludge　fermentation　mixture　as　the　carbon　source,　the　activities　of　ammonia-oxidizing　bacteria　(AOB)　and　nitrite-oxidizing　bacteria　(NOB)　were　inhibited　at　the　beginning.　After　16　days,　the　activity　of　AOB　began　to　recover　rapidly,　but　the　activity　of　NOB　was　still　inhibited.　The　specific　nitrate　production　rate　(SNaPR,　N/VSS)　decreased　from　0.179　1　g•(g•d)-1　to　0.007　8　g•(g•d)-1.　At　the　same　time,　the　nitrite　accumulation　rate　increased　from　8.12%　to　91.42%　and　remained　stable.　The　sludge　fermentation　mixture　was　separated　into　sludge　fermentation　liquid　and　sludge　fermentation　sediment.　The　changes　in　nitrification　activity　by　adding　different　types　of　fermentation　products　were　investigated.　The　results　showed　that　the　activity　of　NOB　decreased　in　the　experimental　group　fed　with　the　sludge　fermentation　mixture　and　the　fermentation　liquid.　The　SNaPR　decreased　from　an　initial　0.179　3　g•(g•d)-1　to　0.151　0　g•(g•d)-1　and　0.161　7　g•(g•d)-1,　respectively.　In　the　experimental　group　fed　with　fermentation　sediment,　the　activity　of　NOB　increased.　SNaPR　rose　from　0.179　3　g•(g•d)-1　to　0.186　4　g•(g•d)-1.　Therefore,　the　activity　of　the　NOB　can　be　inhibited　when　the　sludge　fermentation　mixture　and　the　fermentation　liquid　are　used　as　a　carbon　source　in　the　nitrification　process.　In　addition,　the　short-range　nitrification　process　can　be　realized,　which　is　beneficial　to　accelerating　the　reaction　speed　and　saving　investment　in　this　type　of　carbon　source.　©　2020,　Science　Press.　All　right　reserved.