Abstract: As one kind of typical polymer semiconductor, g-C₃N₄ is a promising photocatalyst material with excellent thermal and chemical stability. In this paper, Bi₂S₃/g-C₃N₄ composite catalysts were prepared by hydrothermal method. The composition, morphology, structure and properties of the sample were characterized by XRD, SEM, TEM, UV-Vis and FS, respectively. The catalytic properties of Bi₂S₃/g-C₃N₄ composites were evaluated through degradation of methyl orange(MO) under the condition of simulating solar light. The results showed that the heterojunction structure of the composite catalyst significantly enhanced the photocatalytic performance of g-C₃N₄. The decomposition rate of MO by Bi₂S₃/g-C₃N₄ composite photocatalyst for 3 h was far higher than that of pure Bi₂S₃ and g-C₃N₄, which was 8.9% and 38.6%, respectively, with the highest value of 97.4% when the mass fraction of Bi₂S₃ reached 50%. The mechanism of Bi₂S₃/g-C₃N₄ composites with enhanced photocatalytic activity was studied. The addition of Bi₂S₃ significantly expanded the light absorption range of g-C₃N₄ and the construction of heterojunction with g-C₃N₄, which could promote the effective separation of photogenerated carriers and extend the carrier life, thus improving the photocatalytic performance of Bi₂S₃/g-C₃N₄ composite catalysts.