Aiming　at　the　problem　that　the　ammonia　nitrogen　in　the　effluent　of　the　multi-stage　A/O　technology　is　likely　to　exceed　the　standard　under　low　temperature　conditions,　the　effect　of　exogenous　addition　of　acyl　homoserine　lactone　signal　molecules　(AHLs)　on　the　characteristics　of　the　biofilm　in　the　aerobic　zone　of　the　multi-stage　A/O　technology　at　low　temperature　was　studied.　Results　showed　that　the　addition　of　100nmol/L　hexanoyl　homoserine　lactone　(C6-HSL)　increased　the　biofilm　nitrification　efficiency　by　22.34%,　and　lauryl　homoserine　lactone　(C12-HSL)　increased　the　amount　of　attachment　biomass　by　24.47%,　both　C6-HSL　and　C12-HSL　had　long-term　effects　on　the　nitrification　efficiency　and　biological　adhesion　of　biofilm.　This　was　because　C6-HSL　can　increase　the　aerobic　biofilm　nitrification　activity　by　17.56%　at　low　temperature,　while　C12-HSL　could　increase　the　content　of　protein　(PN)　in　EPS　by　67.37%.　In　addition,　both　C6-HSL　and　C12-HSL　could　promote　the　endogenous　release　of　the　same　signal,　thus　having　a　long-term　positive　impact　on　the　nitrification　activity　and　adhesion　performance　of　biofilm.　The　high-throughput　sequencing　analysis　showed　that　C6-HSL　can　increase　the　abundance　of　Nitrosomonas,　and　thus　enhancing　the　nitrification　activity　of　biofilm　in　R2;　while　the　addition　of　C12-HSL　had　a　greater　impact　on　the　abundance　of　Rhodobacter,　which　was　an　important　reason　for　the　increase　of　PN　content　in　EPS　of　R5　biofilm.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.