Abstract: In the context of the "Dual Carbon" strategy and the land-sea integration policy, there is an urgent need for synergistic control technologies that combine high-efficiency nitrogen removal with low carbon emissions to address the persistent threats of eutrophication and harmful algal blooms caused by coastal nitrogen pollution. Anaerobic ammonium oxidation (Anammox) exhibits significant potential for pollution and carbon reduction in coastal nitrogen control due to its advantages of no external carbon requirement, low aeration energy consumption, and low sludge production. This study systematically reviews the current status of coastal nitrogen pollution and compares the advantages and disadvantages of traditional nitrogen removal technologies and Anammox technology in terms of pollution and carbon reduction. It further analyzes the impact of salinity on the Anammox system from multiple scales, including genomic characteristics, physiological regulation, cellular structure, as well as community interactions. Based on these analyses, a full-chain synergistic pathway of watershed-estuary-coastal sea for pollution and carbon reduction is proposed. The results show that salinity affects the performance of Anammox systems with a phased pattern characterized by "promotion at low salinity, reversible inhibition at moderate salinity, and irreversible collapse at high salinity", and can also form a synergistic inhibitory effect with pollutants such as heavy metals and antibiotics; the marine species Ca. Scalindua achieves intrinsic high-salinity adaptation through K⁺-glutamate osmotic regulation and ladderane lipid membrane structure, whereas the freshwater species Ca. Brocadia and Ca. Jettenia exhibit significantly weaker salt tolerance due to insufficient osmotic regulatory capacity and differences in membrane lipid composition, and require domestication to achieve limited adaptation; and four key regulatory strategies, including inoculum sources optimization, operating parameters adjustment, process innovation, and exogenous enhancement, can effectively ensure the stable operation of the system under high-salinity conditions. Accordingly, the establishment of an integrated technical system encompassing "land-based reduction - interface interception - marine control" will create a full-chain management pathway from source to end, which will effectively drive the transformation and upgrading of China’s coastal nitrogen pollution control toward a "low-carbon, high-productivity" paradigm and provide a solid technical foundation for achieving synergistic pollution and carbon reduction.