Abstract: Using thiourea and cadmium nitrate tetrahydrate as precursors, the mass ratios of graphite phase carbon nitride(g-C₃N₄) and CdS with low ratio and high ratio were designed in this experiment. The CdS-g-C₃N₄ composite photocatalysts were prepared by simple soft chemical method. Their structures and properties were characterized by SEM, XRD, UV-visible diffuse-reflectance spectrum (UV-Vis DRS), FTIR and physical adsorption. The photocatalytic activity of the CdS-g-C₃N₄ composite photocatalyst under visible light was investigated by photocatalytic degradation experiments of NO. The results show that CdS-g-C₃N₄ composite photocatalyst with low CdS mass ratio has the best degradation effect when mass ratio of CdS to g-C₃N₄ is 7%, and the degradation rate is 31%; among the CdS-g-C₃N₄ composite photocatalysts with low g-C₃N₄ mass ratio, the sample with 5% mass ratio of g-C₃N₄ to CdS has the best degradation performance of 36%. When the mass ratio of CdS to g-C₃N₄ is 4:1 in a large proportion range, the degradation efficiency is the highest, reaching 33%. Moreover, when the mass ratio of g-C₃N₄ to CdS is 5%, the CdS-g-C₃N₄ composite photocatalyst has good stability and best degradation effect.