Semiconductor heterojunction photocatalysts have attracted much attention because of their great application prospects in solar energy utilization and conversion. Rational construction of heterostructure with two or more semiconductor materials can combine the advantages of multi-components to simultaneously improve the photo-induced charges separation, expand the visible light absorption range, and maintain the high redox capacity of photocatalysts. Recently, constructing of g-C3N4-based heterostructure has become a hot research topic due to the multiple merits of g-C3N4, such as facile synthesis, high stability, unique optical and electrical characteristics. This review focuses on the recent research on the modification of g-C3N4-based heterojunction photocatalysts and reviews three heterojunction structures (g-C3N4-based type-Ⅱ heterojunction, g-C3N4-based Z-scheme heterojunction and g-C3N4-based type of S-scheme heterojunction) according to the different charge transfer paths of g-C3N4 and other semiconductors, and their applications in environmental restoration and energy. Finally, the existing problems of g-C3N4-based heterojunction photocatalysts are summarized and prospected.