The mechanism of SO2 removal from a CO2/SO2 gas mixture in a copper benzene-1, 3, 5-tricarboxylate (Cu-BTC) material is investigated at the molecular level by the grand canonical Monte Carlo method. The effects of seven kinds of force-field relationships among CO2, SO2 and Cu-BTC on the selectivity for a SO2/CO2 gas mixture at different temperatures are studied in detail. The accuracy of the simulation model is validated by the experimental data. The results show that more SO2 molecules are adsorbed than CO2, and the electrostatic interactions involving SO2 are more sensitive to temperature than CO2 is. The multilayer desorption for SO2 and CO2 occurs in large-square channels. The effect of the electrostatic interactions involving SO2 is stronger than the interactions of CO2. The forms of CO2 and SO2 adsorption in Cu-BTC with electrostatic interactions are Cu2+∙∙∙OCO and Cu2+∙∙∙OSO, respectively.