Abstract: The structural and adsorption properties of Cu(100)/H surface were studied using density-functional theory (DFT) and projector-augmented wave (PAW) method. It was concluded that atomic hydrogen was adsorbed on the four- fold hollow (FFH) site with a perpendicular distance of 0.052 nm from the outmost Cu layer for a Cu(100)c(2×2)/H geometry. The bond length between H atom and substrate was calculated to be about 0.189 nm. In this adsorbate-substrate system the surface work function was predicted to be about 4.47 eV, which was almost identical to that of a clean Cu(100) surface. The total-energy calculations showed that the chemisorption energy of atomic hydrogen in the case of Cu(100)c(2×2)/H surface was about 2.37 eV with respect to an isolated atomic hydrogen as reference. The hydrogen adsorption on Cu(100) surface yielded the hybridization between surface Cu atoms and adsorbed H, and gener- ated the surface localized states at -0.8 eV relative to Fermi energy EF. This system was modeled at different coverages using p(1×1), p(2×2), and p(3×3) geometries of hydrogen atoms adsorbed on the FFH sites of the Cu(100) surface. The corresponding equilibrium geometries were obtained by total energy and Helleman-Feynman force conjugate-gradient optimizations. In the regime of lower H coverages, the hybridization between adsorbed hydrogen and substrate displayed a type of Cu(S)-H-Cu(S-1) mixing.