Abstract: The coastal area is an important land reserve. However, the saline-alkaline soil in coastal area is characterized by poor soil structure, low nitrogen use efficiency, and obviously seasonal and annual variation in sodium salinity changes which has resulted in an unique soil nitrogen cycle process. The sodium salinity is an important factor influencing the nitrogen cycle, so it is of great theoretical value to clarify its influence on ammonia volatilization and denitrification rate. In this study, cultivation experiments were established with five sodium salinity gradient, namely < 1, 1, 2, 4, and 10 g·kg^-1, to study the effects of salinity on ammonia volatilization and denitrification in coastal soil. Ammonia volatilization and denitrification rates and related water and soil environmental parameters were measured. The results show that high salinity gradient not only reduced the NH₄⁺ adsorption capacity of soil and promoted the release of NH₄⁺ into the water, but also affected pH and nitrogen concentration. The soil environment became alkaline. Alkaline environment promoted the conversion of NH₄⁺ to NH₃, and the ammonia volatilization rate increased significantly. Soil denitrification rate decreased obviously with increasing salinity. The study also found a significant negative correlation between salinity (Na⁺ concentration) and abundance of denitrifying bacteria (nirK and nosZ genotypes). High salinity inhibited microbial activity and reduced denitrification rate.