Efficient　nitrogen　removal　via　the　Anammox　process　at　low　temperatures　is　challenging,　as　it　relies　heavily　on　the　maintenance　of　Anammox　activity　and　biomass.　In　this　study,　a　novel　combination　of　biological　immobilization　and　cold　shock　treatment　was　successfully　applied　to　enhance　specific　Anammox　activity　(SAA)　and　biomass　retention　under　different　low　temperatures.　The　results　indicated　that　the　gel　particles　immobilizing　low　cold-shock　biomass　(only　0.53　g/L)　achieved　superior　SAA　and　exhibited　excellent　mechanical　strength　at　25-5　degrees　C.　Additionally,　the　SAA　and　mass　transfer　performance　of　the　immobilized　cold-shock　particles　were　significantly　influenced　by　particle　size,　with　the　optimal　range　determined　to　be　3.2-4.0　mm.　Consequently,　immobilized　cold-shock　particles　(M1)　were　prepared　with　an　optimal　biomass　content　of　0.53　g/L　and　a　particle　size　of　3.2-4.0　mm.　At　low　temperatures　of　10-5　degrees　C,　the　M1　particles　demonstrated　in-situ　nitrogen　removal　efficiencies　of　52　%-72　%　and　ectopic　SAA　values　of　3.0-4.5　mu　mol/(g　VSS　&　sdot;h),　markedly　outperforming　non-immobilized　cold-shock　granular　sludge　(M0).　This　was　attributed　to　enhanced　biomass　retention　and　improved　ammonium　conversion　kinetics　facilitated　by　immobilization,　particularly　at　10　and　5　degrees　C.　Moreover,　the　higher　abundances　of　Candidatus　Kuenenia　and　Candidatus　Brocadia　within　M1　particles　were　critical　for　sustaining　nitrogen　removal　performance　under　extreme　low-temperature　conditions.　Importantly,　the　upregulated　expression　of　cold　proteins　(CspA,　CspB,　and　PpiD)　and　the　increased　content　of　C18[5]-ladderane　lipids　in　M1　particles　significantly　contributed　to　the　enhanced　lowtemperature　adaptability　of　the　cold-shock　sludge.