The bimetallic nanoparticles with core-shell structure have attracted much attention due to the excellent catalytic performance recently. We examined the thickness effect of the Pd overlayer/shell on Cu substrate/core on the catalytic ability of the overlayer using first-principle calculations and d-band center theory. It is found that overlayer thickness has the important effect on the d-band center of Pd layer. There is a quasi-linear relationship between the adsorption energies of O, O-2, and CO and energy level of d-band center which is modulated by the overlayer thickness. The energy barriers of isolated O-2 dissociation and CO oxidation are found to have an opposite trend with the shift of the d-band center. With this rule, the dissociation of 02 with the assistant of nearby CO is found to be easier on the surface of 2L-Pd/Cu(111). (C) 2017 Elsevier B.V. All rights reserved.