Low　temperature　is　one　of　the　obstacles　in　mainstream　anammox.　This　study　aimed　to　evaluate　the　stability　of　a　step-feed　bioreactor　dominated　by　denitratation/anammox　(PD/A)　for　treating　municipal　wastewater　with　decrease　in　temperature　(21.5　degrees　C　-＞　12.6　degrees　C).　During　long-term　operation,　nitrogen　removal　efficiency　(NRE)　was　improved　from　72.2%　(21.5　degrees　C　-＞　14.9　degrees　C)　to　77.2%　(stable　at　13.9　degrees　C)　with　influent　and　effluent　total　inorganic　nitrogen　of　44.6　and　10.1　mg　N/L.　Better　low　temperature　tolerance　of　nitrate　reduction　than　nitrite　reduction　enhanced　denitratation　and　increased　nitrite　substrates　for　anammox.　Microbial　structure　analysis　revealed　that　Ca.　Brocadia　increased　by　167%　and　reached　0.27%　on　biofilm　at　low　temperature.　Finally,　anammox　contri-bution　improved　from　41.8%　to　60.2%,　saving　organic　carbon　for　denitrification,　which　was　responsible　for　better　NRE.　Moreover,　Ferribacterium,　Dechloromonas,　and　Thauera　were　the　major　denitrifiers　distributed　in　suspended　sludge.　Overall,　this　study　provides　an　optimistic　prospect　for　promoting　anammox　in　mainstream　applications　at　low　temperature.