The water-gas shift reactions (WGS) used to produce hydrogen in industry are usually catalyzed by iron based catalysts, in which the Fe3O4 was confirmed to be the catalytically active phase of iron oxide. In this work, based on the first-principle simulations, we theoretically study the relation between the dopant segregation and activities of the doped Fe3O4 for adsorbing CO. The surface electronic structure is proved to be a fundamental criterion for CO adsorption on doped Fe3O4 surfaces, which can be obtained by theoretical calculations. The surface segregation of dopants generally determine the effects of dopants on the surface properties, and the CO adsorption aims at the special reaction of WGS. It is worth emphasizing that, for a series of experiments on doped Fe3O4 catalyzed WGS, a unified explanation can be given based on the present results. Our theoretical calculations are well consistent with the recent experimental results at around 400 degrees C. Therefore, segregation could have decisive roles on the nature of WGS catalysis by iron oxides. This work is instructive for exactly depicting the catalytic activities of materials based on first-principle calculations, and is also helpful to search highly active catalysts. (C) 2018 Elsevier Inc. All rights reserved.