Photocatalysis, as a green and efficient energy conversion and utilization technology, has attracted widespread attention. Due to its limited use of sunlight as energy input to solve environmental and energy problems, it has broad application prospects. Photocatalyst materials are the key to the development of photocatalysis technology, and the development of new visible light photocatalysts has become a new trend in the development of photocatalysis technology. WO3, as a transition metal oxide semiconductor material, has good visible light response ability and is one of the ideal photocatalytic materials. However, the low efficiency of photo generated charge separation has always hindered its development. Compared to WO3, its hydrated form (WO3·nH2O) is highly favored by researchers due to its higher charge transfer separation efficiency. This article systematically summarizes and organizes the application and research progress of WO3·nH2O materials in the field of photocatalysis in recent years. Firstly, the crystal structure of WO3·nH2O photocatalyst was introduced, then the effect of water of crystallization on the photocatalytic activity of WO3 was analyzed from the perspective of energy band structure, and the preparation methods of WO3·nH2O and WO3·nH2O based modified photocatalyst were emphatically described. Finally, the applications of WO3·nH2O and its constructed composite materials in water desorption hydrogen, CO2 reduction, and degradation of dye pollutants were summarized, and the development prospects were also discussed. This work aims to provide useful references for promoting the development of WO3·nH2O photocatalytic systems.