The photocatalytic materials of Ce∶ZnO composite powder with higher photocatalytic activity was prepared by sol-gel method. The crystal type and structure, free radical type and content, and photocatalytic efficiency of the prepared powder samples were characterized by X-ray diffraction, electron paramagnetic resonance and ultraviolet visible spectroscopy. X-ray diffraction test results of the composite samples show that with the increase of doping concentration, the characteristic peaks of (111) and (200) crystal plane of CeO2 are detected successively, and the intensity of the diffraction peaks gradually increases. In addition, appropriate doping (c(Ce3+)=2%) can reduce the grain size of ZnO crystal. The results of electron paramagnetic resonance test show that there are three kinds of free radicals in Ce∶ZnO composite photocatalytic material, which are Zn-H complex, positive monovalent oxygen vacancy and superoxide ions adsorbed on the surface of CeO2. Ultraviolet visible test shows that appropriate doping (c(Ce3+)=2%) could effectively improve the photocatalytic activity of ZnO catalyst. Based on the analysis of electron paramagnetic resonance and ultraviolet visible test results, the doping of Ce3+ provides more electrons for O2 when it is converted to Ce4+, on the other hand, the generated CeO2 has a strong oxygen absorption capacity. The photocatalytic activity of ZnO is improved by increasing the utilization rate of O2 and generating more active free radicals. In the experiment, the influence process of Ce3+ doping on the synthesis of free radicals in ZnO materials was successfully characterized by electron paramagnetic resonance and X-ray diffraction techniques, and the electron transfer process in the photocatalytic degradation of methyl orange by Ce∶ZnO composites was reasonably explained by ultraviolet visible technology.