The new method for separating drained coal bed methane (CBM) is based on gas hydrate formation. The thermodynamic parameters of incipient hydrate formation for the CH4-N2-O2-THF-H2O system were carefully determined. After establishing equilibrium state of three-phase coexistence, CH4 concentrations of vapor phase and that of hydrate phase were determined by GC. The results show that the higher the THF concentration, the larger the CH4 concentration in hydrate phase and the partition coefficient. It can provide the reference for seeking the optimal promoters in the hydrate formation process for the mixed gas.