In this paper, hydrate phase equilibrium data for the CH4/CO2 + water system, CH4 + tetrabutylammonium bromide (TBAB) + water system, CO2 + TBAB + water system, and CH4/CO2 + TBAB + water system were measured at temperature ranged from 273.6 to 294.2 K and pressure ranged from 0.54 to 14.57 MPa with the 1.76 and 14.00 mass fraction of TBAB solutions. The mixture gas hydrate formation equilibrium temperature and pressure were tested by an isochoric pressure-search method. The mixture gas were composed of 67.00 mol % CH4 and 33.00 mol CO2. The experiment results show that at low TBAB concentration (1.76 wt %), TBAB solution have promote effect under low pressure (lower than 3 MPa), and have nonsignificant promote effect at high pressure. The phase equilibrium conditions for CH4/CO2 mixture gas hydrates with TBAB mainly were determined by the concentration of TBAB solution and did not rely on the concentration of CH4/CO2 mixture gas.