Hydrate-based gas separation(HBGS) technology based on tetra n n-butyl ammonium bromide (TBAB) semiclathrare hydrate can be utilized in CO2 separation from biogas. The phase equilibria of semiclathrate hydrates are crucial for the successful industrial application of HBGS technology. In this work, the phase equilibrium data of TBAB semiclathrate hydrate with a 2 6 synthesized binary CO2/CH4 mixed gas (0.5 CO2 and 0.5 CH4 in mole fraction) were reported at five different TBAB concentrations (0.001, 0.01, 0.05, 0.1, and 0.2 mass fraction). The experiments were conducted in the temperature range (278.1 to 292.6) K and pressure range (2.17 to 8.16) MPa using an isochoric method. The agreement between the experimental data and the data reported in the literature indicated the reliability of the apparatus and method. The results showed that there were no obvious thermodynamic promotion effects on the CO2/CH4 mixed gas hydrate phase equilibrium conditions when the mass fraction of TBAB was less than 0.01, while there was a significant affect on the CO2/CH4 mixed gas hydrate phase equilibrium conditions when the mass fraction of TBAB was greater than 0.05. In addition, the results also indicated that the promotion effect of TBAB on the CO2/CH4 gas hydrate formation may be varied as the concentration of TBAB in the aqueous solutions changes.