Bismuth vanadate (BiVO4) is a promising candidate material for photocatalytic hydrogen generation and photocatalytic degradation of organics. BiVO4 has four phases in nature: tetragonal-1, tetragonal-2, orthogonal and monoclinic. In this paper, first-principle calculations were performed to investigate their structural stability, band structures and optical properties. It is illustrated that the stable phase is pressure-dependent and the most stable ones are T-1 (under 0 GPa), T-2 (under 2 GPa) and M phase (under 4, 6 and 8 GPa). BiVO4 in all cases are indirect band-gap semiconductors and the band gaps decrease with increasing pressure. Moreover, the external pressure might enhance hybridization of O 2p, V 3d and Bi 6s orbitals, and shift the band edges to lower energies. As a result, the optical curves, such as, dielectric function, optical reflectivity, absorption coefficient and refractive index, red shift with pressure in the low energy region, and BiVO4 in T-2 and M phases has almost the same optical properties in spite of different lattice structures. So the optical properties of BiVO4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.