The sulfate-methane interface (SMI) is an important biogeochemical indication for the area with high methane flux and gas hydrate occurrence. In this paper, 37 surface cores were collected in the Dongsha Area of northern South China Sea, and the characteristics of SO4^2- and H2 S concentrations change of the pore water and CH4 concentration change of the head- spaces in the sediments were analyzed. Furthermore, the SMI distribution characteristics were discussed and the methane fluxes were calculated using the sulphate change grades in the Dongsha area of northern South China Sea. The results show that there are two gas hydrate potential areas in the study area. One is the Haiyang-4 site in the southern deep water area, and the other is the Jiulong methane reef in the northern shallow water area. The relatively shallow SMI distribution and high methane flux (3.8× 10 ^-3-5.9×10^-3 mmol/(cm^2 • a)) in the Dongsha area, northern South China Sea are similar to the geochemical characteristics in foreign areas where the gas hydrate occurs. It is convinced that the high methane flux is most probably caused by the occurrence of gas hydrate deposit below the seafloor, which indicates there are gas hydrate reservoirs underneath in the Dongsha area, northern South China Sea.