A CuO/ZnO photo-catalyst nanocomposite was successfully prepared by co-precipitation and characterized for investigating its chemical & physical properties by XRD, SEM, EDS, UV-vis (DRS) and PL spectroscopy. The average particle size of CuO/ZnO composite was found to be around 80 nm. The degradation of chlortetracycline hydrochloride pollutants in marine aquaculture wastewater using ZnO and CuO/ZnO was compared and found that CuO/ZnO nanocomposite is more efficient than ZnO. The effects of external factors on the photocatalytic effectiveness of nanocomposite was investigated under visible light. And the degradation conditions of nanocomposite to chlortetracycline hydrochloride was optimized. Based on both ability and efficiency of degradation, and on the cost and availability, 10:2 molar ratio of Zn2+/Cu2+, 0.7 g/L nanocomposite, was found the optimal, in which case the average photo-catalytic degradation rate of chlortetracycline hydrochloride reached 91.10%.