The　low　salinity　caused　by　the　substitution　of　seawater　and　the　overuse　of　deicing　salt　hinders　the　treatment　of　mainstream　wastewater　by　conventional　biological　nitrogen　removal　process.　In　this　experiment,　the　start-up　and　stable　operation　of　partial　nitrification　were　achieved　based　on　a　composite　zeolite　biofilm　(CZB)　and　94.1　%　of　nitrite　accumulation　efficiency　was　obtained　at　low　salinity.　CZB　could　still　maintain　high　biofilm　proportion,　strong　adhesion　and　robust　structure　to　resist　the　impact　of　0.6　%　salinity.　The　enhanced　release　of　C8-HSL　from　the　aqueous　phase　of　the　CZB　increased　the　oxygen　transfer　resistance　of　the　sludge　layer,　thus　reducing　the　oxygen　mass　transfer　efficiency　of　the　sludge　layer　and　inhibiting　NOB　more　effectively.　The　augmented　release　of　C6-HSL　and　C12-HSL　in　the　sludge　phase　(SP)　leads　to　elevated　production　of　protein　and　polysaccharides,　culminating　in　the　development　of　a　more　resilient　microbial　structure.　Meanwhile,　C6-HSL　and　C8-HSL　in　the　SP　of　CZB　promoted　gene　expression,　especially　nitrate　reductase　(Nar),　to　stabilize　the　supply　of　NO2–-N.　Meanwhile,　CZB　reinforced　the　microbial　impact　resistance　by　enhancing　the　tricarboxylic　acid　cycle,　and　awakened　important　gene　(nrfA,　associated　with　dissimilatory　nitrate　reduction　to　ammonium).　This　activation　played　a　vital　role　in　maintaining　the　appropriate　NH4+-N　to　NO2–-N　ratio　in　the　effluent.　Finally,　CZB　eliminated　Nitrospira　from　the　system　and　increased　the　relative　abundance　of　Nitrosomonas　to　12.8　%　at　0.6　%　salinity.　This　method　offered　valuable　theoretical　insights　for　design　and　optimization　of　the　partial　nitrification　process　for　treating　mainstream　low-salinaty　wastewater.　©　2023　Elsevier　B.V.