Nitrogen　removal　from　saline　municipal　wastewater　has　recently　attracted　attention;　thus,　developing　energy-efficient　technology　such　as　anaerobic　ammonium　oxidation　(anammox)　for　advanced　nitrogen　removal　of　hypersaline　wastewater　is　significant.　In　this　study,　the　long-term　salt　adaptation　and　evolution　mechanisms　of　an　anammox-based　process　driven　by　both　nitritation　(NH4+→NO2—,　PN)　and　denitratation　(NO3—→NO2—,　PD)　were　investigated　under　salinities　ranging　from　1.0%　to　3.0%　(10–30　g　NaCl/L).　At　1.0%　salinity,　PN　evolved　into　the　major　nitrite　production　pathway　with　thorough　suppression　of　nitrite　oxidation.　At　1.5%　salinity,　nitrite　reduction　was　inhibited　along　with　suspended　sludge　loss　due　to　poor　sludge　settleability.　Under　2.0%　salinity　with　only-biofilm,　the　highest　nitrogen　removal　efficiency　(81.2%)　was　observed　with　influent　and　effluent　total　inorganic　nitrogen　concentrations　of　44.5　and　8.2　mg　N/L,　respectively.　Notably,　results　showed　that　anammox　bacteria　occupied　up　to　1.07%　of　the　microbial　community　(qPCR:　1.14×1011　copies/(g　dry　sludge))　and　has　strong　adaptability　to　salinity.　With　salinity　increases,　anammox　contribution　kept　over　85%　and　Ca.　Kuenenia　(0.57%→0.22%)　was　more　tolerant　than　Ca.　Brocadia　(0.46%→0.02%).　Metagenomic　sequencing　revealed　that　the　multiple　nitrite　substrates　production　by　Nitrosomonas　(amoA-enriched),　Denitratisoma　and　Denitromonas　(narG-enriched)　guaranteed　the　high　anammox　contribution.　This　study　provides　a　multifaceted　understanding　of　the　anammox-based　process,　which　can　enable　improved　application　in　real　saline　wastewater　treatment.　©　2023　Elsevier　B.V.