Abstract: Photocatalysis, recognized as an eco-friendly and efficient energy conversion and utilization technology, has garnered widespread attention owing to its potential to address environmental and energy-related challenges. Its capacity to harness sunlight as an energy source makes it particularly promising. Photocatalytic materials are central to the advancement of photocatalytic technology, and the emergence of new visible-light-responsive photocatalysts represents a noteworthy trend in this field. WO₃ is a semiconductor material composed of transition-metal oxides. It exhibits excellent responsiveness to visible light and is considered to be an ideal photocatalytic material. However, the persistent issue of low photogenerated charge separation efficiency has hindered their development. In contrast to pure WO₃, its hydrated form, WO₃·nH₂O, has garnered considerable interest from researchers because of its enhanced charge transfer and separation efficiency. This study comprehensively reviews recent applications and research progress in photocatalysis using WO₃·nH₂O. This study introduces the crystal structure of WO₃·nH₂O photocatalysts and analyzes the impact of crystal water on WO₃. This analysis covered the crystal structure, charge transfer, separation, and band structure. The study then extensively discusses the preparation methods for WO₃·nH₂O and modified photocatalysis based on WO₃·nH₂O, with particular emphasis on elucidating these methods. Finally, this study summarizes the diverse applications of WO₃·nH₂O and its composite materials in water desorption for hydrogen production, CO₂ reduction, and dye pollutant degradation. In addition, it delves into the prospects for future development of these materials. The overarching goal of this study was to serve as a valuable reference for advancing WO₃·nH₂O photocatalytic systems.