Stable　sewage　nitrogen　removal　with　nitrogen　removal　efficiency　of　87.5　+/-　2.2%　was　achieved　in　a　partial　nitrification-anammox　(PNA)　biofilm　system　at　low　temperatures　(12.8-16.3　degrees　C).　High-throughput　sequencing　analysis　indicated　that　the　microbial　community　structure　in　the　sequencing　batch　biofilm　reactor　(SBBR)　remained　reasonably　stable.　Candidatus　Brocadia　was　the　only　detected　anammox　genus　and　remained　stable　at　0.3-0.5%.　Some　psychrotolerant　microorganisms　that　could　secrete　cryoprotective　extracellular　polymeric　substances　(EPS),　including　Flavobacterium　and　Thermomonas,　were　enriched　at　low　temperatures.　This　could　be　conducive　to　the　stable　operation　of　the　PNA-SBBR.　Moreover,　according　to　the　EPS　composition　and　characteristics　analysis,　the　secretion　of　tightly-bound　EPS　that　bound　to　the　cell　surface　containing　plentiful　protein　was　stimulated　at　low　temperatures,　further　improving　the　system　stability.　Overall,　the　reasonably　stable　microbial　community　structure,　enrichment　of　psychrotolerant　microorganisms,　and　increased　secretion　of　EPS　could　play　important　roles　for　stable　sewage　nitrogen　removal　at　low　temperatures.