Abstract: In order to expand the sunlight absorption range of BiOCl and obtain more efficient photocatalyst, Graphite phase carbon nitride (g-C₃N₄)/BiOCl (2D/2D) composite photocatalyst was prepared by hydrothermal method and characterized in detail. The results of structural and morphology characterization show that BiOCl nanosheets are deposited on the layered g-C₃N₄ surface to form 2D/2D face-face composite structure. The analysis of photoelectric chemical properties shows that the formation of heterostructure can effectively expand the frequency range of light absorption and promote the separation and migration of photocarriers, which is conducive to the improvement of photocatalytic performance. The results of photocatalytic degradation of RhB by xenon lamp (500 W) show that the photocatalytic degradation activity of g-C₃N₄/BiOCl heterojunction is much higher than that of g-C₃N₄ and BiOCl alone. Among them, 9wt%g-C₃N₄/BiOCl shows the most superior photocatalytic activity, and the degradation rate of RhB is 94% within 180 min, and the apparent rate constant K_app value of 9wt%g-C₃N₄/BiOCl is 5.7 and 3.6 times that of g-C₃N₄ and BiOCl. At the same time, the photocatalytic mechanism of g-C₃N₄/BiOCl heterojunction was studied, and the photocatalytic degradation mechanism of RhB under dye sensitization was proposed by combining the electronic structure of the composite catalyst and free radical capture experiment.