Inspired by the recently experimental discovered that the single-atom Pd-1/g-C3N4 catalyst exhibited higher ethylene selectivity for hydrogenation of acetylene, we systematically investigate the mechanism of such reactions over Pd-1/g-C3N4 by using the B3LYP method of density functional theory. We found that Pd-1/g-C3N4 can catalytic acetylene hydrogenation with high of selectivity but low of activity energy, which is consistent with the experimental results.Graphical AbstractThe diagram of the whole reaction path over single-atom Pd-1/C3N4 catalyst and the corresponding energy barrier at each step [GRAPHICS] .