This article provides a comprehensive review of WO3-based composite photocatalysts, focusing on their synthesis, catalytic mechanisms, and diverse applications. Photocatalysis, an emerging "green" energy conversion technology, converts solar energy into chemical energy, showing great potential in environmental purification and clean energy production. WO3, with its good visible light response and excellent valence band hole oxidation properties, is a favored photocatalyst. Recent research has shown that WO3-based composite photocatalysts have wide applications, including CO2 reduction, hydrogen production, nitrogen fixation, and pollutant removal. The article systematically summarizes the structural properties, preparation methods, and structure-activity relationships of WO3-based composite photocatalysts. It also discusses the current application status of these materials and analyzes their development prospects. The article begins by highlighting the environmental issues caused by fossil fuel use and the need for clean renewable energy. It then discusses the development of photocatalyst materials, with WO3 being a promising candidate due to its abundance, nontoxicity, and efficiency. WO3 has a band gap of 2.4-2.8 eV, enabling it to respond to visible light. However, its conduction band edge is more positive than the reduction potential of H+, limiting its application in hydrogen production. To overcome these limitations, various modification strategies have been applied, including doping, photosensitization, and composite construction. Composite materials have become a major focus of recent research, with nearly half of the modification efforts in the past five years focused on composite strategies. The article then discusses the structure and physicochemical properties of WO3, including its crystal phases and the perovskite-like ReO3 structure. It also reviews the synthesis strategies for WO3-based composite photocatalysts, their structural configurations, and the mechanisms of different configurations in photocatalytic reactions. Finally, the applications of these photocatalysts in CO2 reduction, hydrogen production, nitrogen fixation, and environmental purification are summarized, along with the current status and future development directions of WO3-based composite photocatalysts.This article provides a comprehensive review of WO3-based composite photocatalysts, focusing on their synthesis, catalytic mechanisms, and diverse applications. Photocatalysis, an emerging "green" energy conversion technology, converts solar energy into chemical energy, showing great potential in environmental purification and clean energy production. WO3, with its good visible light response and excellent valence band hole oxidation properties, is a favored photocatalyst. Recent research has shown that WO3-based composite photocatalysts have wide applications, including CO2 reduction, hydrogen production, nitrogen fixation, and pollutant removal. The article systematically summarizes the structural properties, preparation methods, and structure-activity relationships of WO3-based composite photocatalysts. It also discusses the current application status of these materials and analyzes their development prospects. The article begins by highlighting the environmental issues caused by fossil fuel use and the need for clean renewable energy. It then discusses the development of photocatalyst materials, with WO3 being a promising candidate due to its abundance, nontoxicity, and efficiency. WO3 has a band gap of 2.4-2.8 eV, enabling it to respond to visible light. However, its conduction band edge is more positive than the reduction potential of H+, limiting its application in hydrogen production. To overcome these limitations, various modification strategies have been applied, including doping, photosensitization, and composite construction. Composite materials have become a major focus of recent research, with nearly half of the modification efforts in the past five years focused on composite strategies. The article then discusses the structure and physicochemical properties of WO3, including its crystal phases and the perovskite-like ReO3 structure. It also reviews the synthesis strategies for WO3-based composite photocatalysts, their structural configurations, and the mechanisms of different configurations in photocatalytic reactions. Finally, the applications of these photocatalysts in CO2 reduction, hydrogen production, nitrogen fixation, and environmental purification are summarized, along with the current status and future development directions of WO3-based composite photocatalysts.