With the depletion of fossil fuels and environmental contamination, photocatalytic H2 production has become an essential issue. Co‐catalysts play a critical role in improving photocatalytic H2 generation of photocatalysts. However, co‐catalysts frequently need additional synthesis steps for loading on the surface of photocatalysts, and the interface contact between the co‐catalyst and the photocatalyst is insufficient. Herein, a CdS/MoS2 nanooctahedron heterostructure is prepared through the in situ sulfidation of CdMoO4 nanooctahedrons. MoS2 as the co‐catalyst provides active sites for H2 generation and enhances the separation of photo‐generated carriers. Furthermore, the sulfidation of CdMoO4 precursors ensures a tight contact interface by S atoms between CdS and MoS2, which is beneficial to the electrons transfer from CdS to MoS2, thus markedly improving the photocatalytic H2 evolution activity. The obtained optimum CdS/MoS2 nanooctahedrons exhibit a better photocatalytic H2 generation activity than those of pure CdS, pure MoS2, and even CdS/MoS2 by hydrothermal synthesis under visible light irradiation. In addition, solar‐driven biomass upgrading of furfural alcohol, bacterial cellulose membrane, bioplastic wastes upgrading of polylactic acid (PLA), polyethylene terephthalate (PET), and their reforming to H2 are also performed and demonstrate an inexpensive route to drive aqueous proton reduction to H2 through waste biomass oxidation.