BiVO4 and few-layer black phosphorus (BP) are both photocatalysts that are responsive to visible light, and heterocomposites thereof enable overall water splitting to generate H2 and O2 with the aid of sunlight. In this work, first-principles calculations of BP/BiVO4 heterostructures were carried out to elucidate the detailed electronic structures and carrier properties, including the dependence on the local structure of the surface as well as the number of BP layers. Our findings indicate that the electronic structure strongly depends on the particular BiVO4 surface; the combination of BP with the BiVO4(110) surface is predicted to form a type-I heterojunction, whereas the BiVO4(010) surface yields a suitable band alignment with BP. In the latter, charge transfer can occur efficiently because of the local, site-dependent electric field between each V site and neighboring phosphorus atoms. Furthermore, the computational results on BP layer dependence suggest that the photocatalytic efficiency of BP/BiVO4 may be experimentally controlled using multiple layers of BP because the electric field at the interface can be strengthened and the visible light absorption is enhanced, although the valence band edge of BP may become unsuitable for Z-scheme with more than a few layers in the heterosystem.