Investigation of interfacial mass transfer by means of numerical simulation is a promising field. In the present work, the Rayleigh convection of the CO2-ethanol absorption process was simulated using a random-disturbance model based on the lattice Boltzmann method and the results were compared with the Schlieren observation for validation. It was found that the simulation method was superior for capturing the characteristics of the absorption process. A correlation was then proposed to predict the mass transfer coefficient based on Reynolds mass flux, scalar fluctuation variance, and its dissipation rate, and the correlation was found to be superior to existing methods in terms of phase difference. In this correlation, the mass transfer coefficient was linked with computational mass transfer for the first time.