The model, i.e., the thermodynamic model, focused on the cubic-plus-association equation of state combined with the Wong-Sandler mixing rule with six parameters is presented (CPA-WS). The model confirmed that the inert association scheme is more suitable for carbon dioxide (CO2) than the 3B association scheme, for the level equilibrium in the carbon dioxide-water (H2O) system. Meanwhile, the CO2-H2O-sodium chloride (NaCl) system can be reasonably well predicted by using two adjustable parameters of the H2O-NaCl and CO2-NaCl systems. The average absolute relative deviations of the predicted CO2 solubility in H2O and aqueous NaCl solutions of the CPA-WS model are 5.31 and 3.56%, respectively.