In this article a first-principles total energy calculation of the atomic geometry and electronic structure of carbon-monoxide and hydrogen co-adsorbed on Ni(111) p(2×2) surface at a coverage of 0.25 ML is reported. The optimized atomic geometry is in good agreement with the most recently reported LEED experiment on Ni(111) p(2×2)/(CO+H) co-adsorbed system. The carbon-monoxide is predicted to be adsorbed on the hcp site while hydrogen atom occupies the fcc site, and both adsorbates locate on opposite p(1×1) cells within a p(2×2) supercell. The adsorption energy of CO and H in this configuration is 2.81 eV with respect to the CO and H2 molecule and the surface work function is calculated to be 6.28 eV in comparison with 5.23 eV of clean Ni(111) surface. The bond lengths of C—O, C—Ni, and H—Ni are estimated to be 1.19?, 1.96?, and 1.71?, respectively, and the substrate interlayer distance variations, Δd12 and Δd23, are calculated to be +1.6% and +0.4%, respectively. The chemisorptions of CO and H atom on the Ni(111) p(2×2) surface were calculated in the same way and the adsorption heights of CO and H were evaluated to be 1.33? and 0.90?, respectively. The interaction energy between CO and H in the best fit geometry of Ni(111) p(2×2)/(CO+H) system is about 0.60 eV, which could be taken as the essential factor for the realization of Fisher-Tropsch reaction.