By employing the first-principles density functional theory, the band structure, electron density of states and optical properties of the {112} surface of CuIn0.5Ga0.5Se2 (CIGS) are calculated and systematically investigated. Hole barriers can be contributed by the {112} surface of CIGS. Cu vacancies (V-Cu) and the Na that replaces the Cu (Na-Cu) in the {112} surface of CIGS. But V-Cu are not chemically stable and are always occupied by impurities, such as Na. Thus the bandgap and the local built-in potential between sub layers and surface layer are enhanced by the doping of Na. The absorption of infrared light can also be improved by Na-Cu. These results reveal that the properties of the {112} surface is similar to that of grain boundary (GB) existed in CIGS. And properties of the {112} surface may clarify the origin of the local built-in potential existed between grain boundary (GB) and grain interior (GI) in polycrystalline CIGS and provide ways to increase its efficiency. (C) 2015 The Electrochemical Society. All rights reserved.