The oxygen evolution reaction (OER) is regarded as one of the key issues in achieving efficient photocatalytic water splitting. Monoclinic scheelite BiVO4 is a visible-light-responsive semiconductor which has proved to be effective for oxygen evolution. Recently, the synthesis of a series of monoclinic BiVO4 single crystals was reported, and it was found that the (010), (110), and (011) facets are highly exposed and that the photocatalytic O2 evolution activity depends on the degree of exposure of the (010) facets. To explore the properties of and photocatalytic water oxidation reaction on different facets, DFT calculations were performed to investigate the geometric structure, optical properties, electronic structure, water adsorption, and the whole OER free-energy profiles on BiVO4 (010) and (011) facets. The calculated results suggest both favorable and unfavorable factors for OER on the (010) and the (011) facets. Due to the combined effects of the above-mentioned factors, different facets exhibit quite different photocatalytic activities.