Density functional calculation has been used to study the influences of atomic arrangements of Zn/Pd(111) bimetallic surface on the activity and selectivity of formic acid decomposition processes. A high catalytic selectivity for non-CO pathway of formic acid decomposition was found on Zn-rich Zn/Pd(111) surface with an isolated Pd trimer ensemble; and the O-H activation is the predominant process via the reaction of while C-H activation is highly endothermic in the hydroxycarbonyl formation reaction via . Moreover, the high CO tolerance was found on the Zn-decorated Pd(111) surface with small Pd ensembles, and the desorption energy of CO is reduced to similar to 1.4 eV. These results indicate the electrocatalytic activity of Pd can be improved by incorporating the post transition metal of Zn through adjusting atomic composition and geometric distribution on surface. Graphical Abstract.