In this paper, a mathematical model is developed to simulate the physical–chemical coupling process of supercritical carbonation in cement-based materials. This model takes into account the rate of chemical reaction, mass conservation for gas–liquid two phase flow, diffusion and dispersion of CO2 in water, energy conservation for porous medium and the solubility of CO2 in water. Numerical results are obtained and compared with experimental results. The degree of carbonation, temperature, gaseous pressure, moisture content and saturation of water within the material are predicted and presented. The influence of material saturation, temperature and pressure of supercritical CO2 on carbonation depth is investigated through parametric studies. The comparisons with test results suggest that the coupled model can be used to predict carbonation process of cement-based materials under supercritical conditions.