Doping strategy has demonstrated to be one effective approach to modify the band structure of oxide semiconductors, which usually introduce the discrete mid-gap states to extend the light absorption range. However, the localized mid-gap states have limited benefit to photocatalytic activity. In the present work, the density functional theory (DFT) calculations indicate that indium (In) doping in bismuth oxyhalides (BiOXs, X = F, Cl, Br and I) could overcome this issues through increasing the light absorption and improving the potential for water reduction. Substitutional In (Subln) doping in BiOXs (X = F, Br and I) leads to band gap narrowing through shifting the conduction band edge to lower energies, which can improve the light absorption without creating the mid-gap states. Specifically, the Subln-doped BiOCl increases band gap due to the increased energy levels of the In 5s states. Although Subln-doped BiOCl cannot extend the light absorption of the photocatalyst into the visible light spectrum, it indeed improved the necessary redox potentials for splitting water and preventing from trapping charge carrier. We believe that the DFT calculation results on Subln-doping BiOXs will guide the further development of highly efficient semiconductor photocatalysts. (C) 2018 Elsevier B.V. All rights reserved.