A mechanistic model based on liquid irrigation feature is proposed for predicting mass transfer performance of sheet-metal structured packings. The model was used to simulate mass transfer performance of Gempak 4A structured packings for CO2 absorption using NaON aqueous solutions. A very good agreement between the simulation results and the experimental data acquired from a pilot CO2 absorption unit was found under ranges of process parameters including liquid load, initial liquid distribution pattern, and liquid temperature. In comparison with published mass transfer correlations, the proposed model can effectively handle the prediction in a wider range of the liquid load.