A　novel　two-stage　partial　nitrification-anammox　(PN-A)　process　was　developed,　achieving　nitrogen　removal　from　low　carbon/nitrogen　ratio　municipal　sewage　under　two　typical　operational　modes　and　seasonal　ambient　temperatures.　When　complete　nitritation-anammox　was　performed　at　temperatures　greater　than　19.4　degrees　C,　the　effluent　concentration　of　total　inorganic　nitrogen　(TIN)　was　4.1　mg/L,　corresponding　to　a　nitrogen　removal　efficiency　(NRE)　of　94.3　%.　In　contrast,　when　partial　nitritation-anammox　was　performed　at　temperatures　below　19.4　degrees　C,　the　effluent　TIN　was　12.3　mg/L,　corresponding　to　a　NRE　of　83.6　%.　The　relative　abundance　of　Nitrosomonas　and　Nitrosomonadaceae　increased　from　0.02　%　to　0.28　%,　while　Ca.　Brocadia　decreased　from　1.85　%　to　1.30　%,　with　the　contribution　of　anammox　to　nitrogen　removal　being　highest　under　low　temperatures　(19.4?　to　13.8?),　at　59.0　%.　This　novel　two-stage　PN-A　process　provides　a　new　approach　for　the　stable　operation　of　wastewater　treatment　plants　(WWTPs)　under　low　ambient　temperatures.