Three-phase equilibrium conditions for forming methane hydrate were experimentally obtained in aqueous single electrolyte solutions containing 3wt% NaCl and 3 wt% MgCl₂. The experimental temperature and pressure ranges were 274.41-291.11K and 2,500-19,050 kPa for pure water, 274.16-287.96K and 2,920-18,090 kPa for NaCl 3wt% solution, 272.86-286.41K and 2,910-11,840 kPa for MgCl₂ 3wt% solution, respectively. The experimental three phase equilibria consisting of solid methane hydrate, liquid water and gaseous methane were compared with the predicted values calculated from the van der Waals-Platteeuw based model. Methane hydrate could be stable under specific temperature and pressure condition that occurs in the ocean floor sediments. Geophysical survey was implemented in the southern area of the East Sea, and the methane hydrate stability field was determined by simultaneously considering temperature, pressure and geothermal gradient obtained from the survey and well data. In the study area, methane hydrates might possibly exist in the sediments below the water depths of about 100 m, and the length of stability field appeared to be located at about 440m beneath the seafloor and varied with the type of electrolytes.