The electronic structures of S/Se atom-doped BiVO4 (010) surfaces and their photocatalytic behavior are studied with the DFT + U approach. Our theoretical results showed that the S/Se atoms preferentially occupy the position of O atoms on the outer surface of BiVO4 (010). Such S atoms generate a nearly delocalized (0.15–0.22 eV) and a delocalized occupying defect energy state (0.32–0.48 eV) above the valence band maximum (VBM), while the Se atoms produce two delocalized occupying defect energy states above the VBM at 0.35–0.44 eV and 0.60–0.65 eV. The delocalized defect states are equivalent to the bridge of electron transition from the VBM to conduction band minimum (CBM) and form an intermediate band semiconductor. These intermediate bands can lead to a strong absorption from visible light to UV regions, resulting in a redshift of the reflectance spectra. The position of the S/Se atoms occupying the O atoms at the outermost position of the (010) external surface plays a major role in improving its photocatalytic performance.