Pure methane and nitrogen form structure I and II hydrate, respectively, and therefore the structure typeof mixed gas hydrate was found to largely depend on their relative gas composition. In addition to the structural differ-ence of size and shape, each hydrate structure shows different capacity to store the guest molecules. In this study, weinvestigated phase and structural behaviors according to the composition of methane+nitrogen gas mixture. Three-phase (H-Lw-V) equilibria of solid hydrate, water-rich liquid and vapor phase containing 25.24mol%, 28.51mol%,31.23mol% and 40.39mol% of methane were determined at various temperatures (in the range from 273.30K to285.05K) and pressures (from 8.325MPa to 20.700MPa). 13C solid-state NMR spectroscopy and powder XRD methodwere performed to identify the formed structure of hydrate samples. The experimental results showed that gas hydrateof the methane+nitrogen mixture changes its structure from sI to sII between 25.24mol% and 28.51mol% of methaneconcentration. These results of phase behavior and structure identification for the mixed gas hydrates are expected tobe very helpful in evaluating the feasibility of exploitation of methane gas from natural gas hydrate and the separationprocess using gas hydrate as a storage-media