Fly ash-CO2 mineralization technology can effectively control gas–solid waste emissions and improve the climate environment. However, rationally describing the evolution mechanism of the fly ash-supercritical CO2 mineralization reaction and accurately predicting the efficiency of the mineralization reaction are of great significance for improving and evaluating the supercritical CO2 mineralization sequestration capacity. Fly ash micro- and nanopore multi-scale effects are the key to influencing the supercritical CO2 seepage-mineralization reaction mechanism. None of the current theoretical models consider the pore multi-scale effects, thus the validity and accuracy of predicting and describing the evolutionary mechanism of supercritical CO2 mineralization rates and efficiencies are questionable. To address this scientific issue, a multi-scale continuous pore structure theoretical model was established based on the structural characteristics of fly ash micro- and nanopores. Additionally, a new model of supercritical CO2 multi-field and multi-scale dynamic mineralization theory was developed by considering parameters such as temperature, pressure, and humidity. The accuracy of the model was verified through the mineralization experiments. The new model effectively describes the dynamic evolution mechanism of supercritical CO2 mineralized fly ash. The effects of parameters such as temperature, pressure, water vapor diffusion coefficient, supercritical CO2 permeability, and pore multi-scale effect on the efficiency and mineralization rate were investigated through numerical simulation. The results showed the following: The mineralization efficiency exhibited a parabolic increase with temperature, with 72℃ being the turning point for the growth rate of mineralization efficiency, and 82℃ being the optimal effective temperature to promote the mineralization efficiency of supercritical CO2. A 3.5-fold increase in supercritical CO2 pressure changes the mineralization efficiency by a maximum of only 0.0493 %. Increasing the water vapor diffusion coefficient by 5 orders of magnitude changes the mineralization efficiency by only 8.3 %. The pore attenuation coefficient increases by 3 orders of magnitude, and the supercritical CO2 mineralization efficiency changes by a factor of 2.27. A model that does not account for pore multi-scale effects overestimates the fly ash- supercritical CO2 mineralization efficiency by a factor of 2.47 at a permeability of 3 × 10-10 m2. Therefore, neglecting the pore continuum multi-scale effect can lead to a serious overestimation of the mineralization efficiency of supercritical CO2.