The Er3+:Y3Al5O12, an upconversion luminescence agent, which is able to transform the visible light to ultraviolet light, was synthesized by nitrate-citric acid method. And then, a novel photocatalyst, Er3+:Y3Al5O12/ZnO composites, was prepared by ultrasonic dispersing and liquid boil method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structural morphology and surface properties of the Er3+:Y3Al5O12/ZnO. Azo Fuchsine dye was selected as target organic pollutant to inspect the photocatalytic activity of Er3+:Y3Al5O12/ZnO. The key parameters affecting the photocatalytic activity of Er3+:Y3Al5O12/ZnO, such as Er3+:Y3Al5O12 content, heat-treatment temperature and heat-treatment time, were studied. In addition, the effects of dye initial concentration, Er3+:Y3Al5O12/ZnO amount and solar light irradiation time were also reviewed, as well as the photocatalytic activity in degradation of other organic dyes were compared. It was found that the photocatalytic activity of Er3+:Y3Al5O12/ZnO was much superior to pure ZnO under the same conditions. Thus, the Er3+:Y3Al5O12/ZnO is a useful photocatalyst for the wastewater treatment because it can efficiently utilize solar light by converting visible light into ultraviolet light.