Ethylene epoxidation reaction to selectively produce the ethylene oxide (EO) is a crucial heterogeneous catalytic chemical process in industry. However, the intrinsic catalytic selectivity depending on the facet of commonly used Ag catalysts is still far from understanding. In this work, we used the periodical density functional theory (DFT) calculations to gain an atomistic insight into the facet-dependent reaction selectivity of the ethylene epoxidation on Ag catalysts. We investigated the adsorption of atomic or molecular oxygen and oxametallacycle (OMC) intermediate, and further study the dissociation of molecular oxygen and the reaction mechanism of ethylene epoxidation on (111), (110), (100), and (211) surfaces of Ag catalysts. Our results indicate that the adsorption of the 0 atom is not facet-dependent under low oxygen coverage. Moreover, although the adsorption of molecular oxygen is facet-dependent, the dissociation of molecular oxygen would not have the essential influence on selectively producing EO in the ethylene epoxidation reaction. In addition, the catalytic selectivity of ethylene epoxidation reaction is facet-dependent, following the order of (110) > (100) > (111) > (211), which is consistent with the order of the adsorption strength of the OMC intermediate. Our results show that the stability of the OMC intermediate has an essential effect on the selectivity to EO in the ethylene epoxidation reaction. We have faith in that our results can provide useful information which would guide the intellectual design of the catalysts for ethylene epoxidation by controlling their morphologies. (C) 2017 Elsevier B.V. All rights reserved.