The Z-scheme heterogeneous photocatalytic system simulates the natural photosynthesis process and can overcome the shortcomings of the single-component photocatalyst, and possess many merits, including increased light-harvesting, spatially separated reductive and oxidative sites, and well-preserved strong redox ability, which benefits the photocatalytic performance. Here we report the fabrication of a novel WO3/MoS2 heterojunction via the hydrothermal method, with the structure, electronic and photocatalytic properties analyzed by means of experimental and theoretical methods. Photocatalytic studies have been conducted on methylene blue dye under visible light in the presence of WO3/MoS2 heterostructure, and the degradation rate was as high as 90% within 60 min of light irradiation. A detailed theoretical study of this system shows that an internal electric field at the interface of the heterojunction was formed directed from MoS2 to WO3, which helps to separate the photogenerated electron-hole pairs efficiently through a direct Z-scheme charge transfer process. This work also demonstrated the significant potential of WO3/MoS2 heterostructure towards hydrogen evolution reaction.