Abstract: Efficient water splitting for H₂ evolution over semiconductor photocatalysts is highly attractive in the field of clean energy. It is of great significance to construct heterojunctions, among which the direct Z-scheme nanocomposite photocatalyst provides effective separation of photo-generated carriers to boost the photocatalytic performance. Herein, Z-scheme hydrated tungsten trioxide/ZnIn₂S₄ is fabricated via an in-situ hydrothermal method where ZnIn₂S₄ nanosheets are grown on WO₃xH₂O. The close contact between WO₃0.5H₂O and WO₃0.33H₂O as well as ZnIn₂S₄ improve the charge carrier separation and migration in the photocatalyst, where the strong reducing electrons in the conduction band of ZnIn₂S₄ and the strong oxidizing holes in the valence band of WO₃0.33H₂O are retained, leading to enhanced photocatalytic hydrogen production. The obtained WO₃xH₂O/ZnIn₂S₄ shows an excellent H₂ production rate of 7200 mol g^-1 h^-1, which is 11 times higher than pure ZnIn₂S₄. To the best of our knowledge, this value is higher than most of the WO₃-based noble metal-free semiconductor photocatalysts. The improved stability and activity are attributed to the formation of the Z-scheme heterojunction, which can markedly accelerate the interfacial charge separation for surface reaction. This work offers a promising strategy towards the design of an efficient Z-scheme photocatalyst to suppress electron-hole recombination and optimize redox potential.