The CDs/ZnO/g-C3N4 composites were prepared by impregnation-thermal polymerization method, and the photodegradation efficiency of Rhodamine B was investigated. The catalyst was characterized and evaluated by means of XRD, TEM, XPS, UV-Vis DRS and FI-IR. The results show that CDs/ZnO/g-C3N4 still maintains the crystal structure of g-C3N4 in the graphite phase, and the ternary components synergistically make CDs/ZnO/g-C3N4 exhibit excellent photocatalytic properties, which degrade Rhodamine B. The effect is better than monomer g-C3N4, ZnO and ZnO/g-C3N4, and the decolorization rate can reach about 70%.