Abstract: Photocatalytic technology is capable of converting CO₂ into valuable hydrocarbon compounds, providing a new way to solve the problems of fossil fuel shortage and global warming. However, conventional semiconductor photocatalysts have limited effects due to their small specific surface area and insufficient CO₂ adsorption capacity. g-C₃N₄ has attracted much attention in the photocatalytic field due to its non-toxicity, high stability, and low-cost properties. Although the photocatalytic efficiency of pure g-C₃N₄ is constrained by the fast complexation of photogenerated electron/hole pairs, small surface area, and insufficient light absorption, the charge separation, surface area, and light absorption of g-C₃N₄ are significantly enhanced by forming a heterostructure with a large bandgap semiconductor. Such g-C₃N₄-based heterostructures include semiconductor-supported, carbon material-supported, non-metal-supported, and metal-organic backbone-supported types, which show great potential in CO₂ photoconversion. However, modified g-C₃N₄-based heterostructures still face challenges in CO₂ photoconversion and require further research and design innovation. This review emphasizes the important role of g-C₃N₄-based heterostructures in an environmentally friendly and sustainable approach to CO₂ reduction.