Thermodynamic properties of TBAB + CO2 + water system are important for using TBAB + CO2 semiclathrate hydrates in some promising hydrate-based techniques. This work is an experimental and modeling study of two fundamental properties in vapor-liquid phase equilibrium of TBAB + CO2 + water, that is, CO2 solubility in TBAB solution and density of CO2-saturated TBAB solution. With the use of a PVT system, CO2 solubility was measured; thus, Henry's constant was obtained at temperatures from 288.1 K to 303.1 K and TBAB mass fraction from 0.10 to 0.40. Our results showed that CO2 is either salted-in or salted-out by the presence of TBAB, depending upon the temperature and TBAB concentration. For the density, we present experimental data for TBAB + water system at T = 283.15 K to 303.15 K with pressures up to 5 MPa. The density of CO2-saturated TBAB aqueous solution was calculated with the help of Duan's model, which takes into account the effect of pressure and temperature to calculate the apparent molar volume of dissolved CO2 in pure water.