Visible light photocatalysts have drawn wide attention due to their great prospect in solving environmental problems, such as air pollution and water pollution. In this work, using first principles study, we report the doping site, formation energy, electronic and optical properties of B, F single doped and co-doped monolayer MoS2. It is found that B and F co-doping can greatly improve the photocatalytic activity of MoS2 in visible light range. This is attributed to the lower recombination rate of photoexcited carriers, stronger oxidation (or reduction) capacity, higher absorption efficiency of visible light and more catalytic active sites. This work helps to understand the intrinsic photocatalytic mechanisms of MoS2, and provides an important guidance to design more efficient MoS2-based visible light photocatalysts. (C) 2020 Elsevier Inc. All rights reserved.