The invention belongs to the technical field of immunoassay and bio-sensation and provides a preparation method of a zeranol photoelectric chemical sensor and application. According to the preparationmethod, ZnO is adopted as a substrate, the surface of the substrate is modified with patterned ZnIn2S4, and because of excellent conductivity and large surface areas, background signals can be effectively reduced. Co doped CdS sensitized ZnO/ZnIn2S4 with a high photoelectric conversion rate grows in situ by using a soaking method. A photoelectric current signal is generated under radiation of anLED lamp of a visible wavelength, Co-Cds and ZnO/ZnIn2S4 are in good band gap matching, and thus the photoelectric signal conversion efficiency of the sensor can be further increased. The sensor is good in specificity, high in sensitivity and low in detection limit and has significant scientific meanings and application values for zeranol detection.