The　differences　in　the　photocatalytic　activity　of　bismuth　vanadate　in　three　crystalline　phases　have　been　investigated　through　calculating　their　electronic　structures　and　optical　properties　based　on　density　functional　theory.　Our　results　indicate　that　zircon-tetragonal　BiVO4　has　a　direct　and　wide　band　gap,　while　monoclinic　BiVO4　and　scheelite-tetragonal　BiVO4　has　indirect　and　narrow　band　gaps.　The　density　of　states　and　atom　populations　of　monoclinic　and　scheelite-tetragonal　phases　are　similar,　but　slightly　different　from　those　of　zircon-tetragonal　phase.　Among　three　phases,　the　monoclinic　BiVO4　possesses　the　largest　dipole　moment　and　the　lightest　effective　mass　of　carriers,　which　can　promote　the　generation　and　separation　of　photo-induced　carriers,　and　subsequently　may　improve　photocatalytic　activity.