The catalytic mechanism of selective hydrogenation of acetylene was researched by quantum mechanics theory and Monte Carlo methods and using Pd-Ag alloy as the active component,Al₂O₃ as the carrier and the as-prepared catalyst as the study object.The relationship of catalyst activity and selectivity with dispersion of Pd-Ag catalyst was obtained.The results showed that the capacity of acetylene desorption from the surface of the catalyst was enhanced,and the formation possibility of ethane from ethylene was reduced with the increase of Ag loading,thereby the selectivity of acetylene hydrogenation was enhanced.The activation energy of H2 dissociation process on the catalyst surface and hydrogenation process of acetylene and ethylene was attained by calculation.The optimal condition of acetylene selective hydrogenation was as follows: temperature (70-80) ℃,and hydrogen partial pressure (0.03-0.04) MPa.