Dinitrogen gas (N₂) production removes fixed N from the marine biosphere; however, questions remain over the relative influence of microbial processes in determining N₂ efflux from coastal sediments. Here, we quantify N₂ production processes and controlling factors along a ～2,500 km continental shelf sediment transect of China via combined molecular and isotopic approaches. We show that denitrification is the dominant pathway of sedimentary N₂ production, which is greatly higher than anaerobic ammonium oxidation. N₂ production rates by denitrification increase with nosZ gene abundance and decrease with bacterial diversity. The effects of temperature and dissolved oxygen on denitrification are mainly through their influence on biotic factors including functional genes, microbial biomass, and bacterial diversity. The rate of anaerobic ammonium oxidation increases with hzsB gene abundance. Temperature, dissolved oxygen, and dissolved organic carbon appear to indirectly affect anaerobic ammonium oxidation rate by regulating hzsB gene abundance. When extrapolated to the entire sampling region, the annual flux of sedimentary denitrification is estimated at ～9.2 Tg N yr^？1. These results improve our understanding of sediment N removal processes and the mechanistic factors that regulate denitrification fluxes.