The microscopic reaction mechanism for CO oxidation on Cu(311) surface has been investigated by means of comprehensive density functional theory (DFT) calculations. The elementary steps studied include O-2 adsorption and dissociation, dissociated O atom adsorption and diffusion, as well as CO adsorption and oxidation on the metal. Our results reveal that O-2 is considerably reactive on the Cu(311) surface and will spontaneously dissociate at several adsorption states, which process are highly dependent on the orientation and site of the adsorbed oxygen molecule. The dissociated O atom may likely diffuse via inner terrace sites or from a terrace site to a step site due to the low barriers. Furthermore, we find that the energetically most favorable site for CO molecule on Cu(311) is the step edge site. According to our calculations, the reaction barrier of CO + O --> CO2 is about 0.3 eV lower in energy than that of CO + O-2 --> CO2 + O, suggesting the former mechanism play a main role in CO oxidation on the Cu(311) surface. (C) 2011 Elsevier B.V. All rights reserved.