We explore the effects of crystal facet on the interfacial structures and properties of the Bi2WO6/BiOCl heterostructures using first-principles calculations. The Bi2WO6 (0 1 0) facet is used to match the BiOCl (0 0 1) and (0 1 0) facets to construct the Bi2WO6(0 1 0)/BiOCl(0 0 1) and Bi2WO6(0 1 0)/BiOCl(0 1 0) heterostructures. We find that the Bi2WO6(0 1 0)/BiOCl(0 0 1) interface has a marginal lattice mismatch compared with the Bi2WO6(0 1 0)/BiOCl(0 1 0) interface. The density of states analyses reveal that the Bi2WO6(0 1 0)/BiOCl(0 0 1) heterostructure has a favorable valence band offset. Moreover, a built-in electric field can be formed at the Bi2O6(0 1 0)/BiOCl(0 0 1) interface. The existence of the favorable band offsets and the electric fields in the Bi2WO6(0 1 0)/BiOCl(0 0 1) heterostructure can facilitate the separation of the photo-generated electron-hole pairs, resulting in the higher photocatalytic performance than the Bi2WO6(0 1 0)/BiOCl(0 1 0) heterostructure. Our results show that the crystal facet has an important effect on the photocatalytic properties of the Bi2WO6/BiOCl heterostructures, and also provide a reference for the design of highly efficient heterostructure photo-catalysts combined with crystal facet engineering.