NO2 is one of the important components in flue gas from combustion in power plants, which together with CO2 and SO2 pollute the atmosphere if released and cause the undesired acid rains. NO2 reacts immediately with H2O upon dissolution, which prevents direct measurements on the physical phase equilibria of the chemical system. Modeling this reacting system is a challenging task due to the complexities arising from the heterogeneous nature of the chemical reaction, the multiple components that are involved in the phase equilibria, ionic dissociation in water, self- and cross-associations among the molecules, and multiple chemical reactions that may occur before reaching the physicochemical equilibria. Therefore, efforts on modeling this NO2/H2O system have been made so far with no satisfactory progress. In this work, we propose a complete model of the system using Perturbed Chain Statistical Associating Fluid Theory (PCSAFT) equation of state (EOS). The model is found to be able to calculate the solubility curves of NO2 in water at various pressures and temperatures, which provide a strong foundation for a later application in flue gas sequestration into aquifers.