At room temperature， CuO nanowires were prepared on Cu substrate by solution method. Subsequently ZnO nanoparticles were grown on the surface of the CuO nanowires by solvothermal method to construct CuO/ZnO composite nanowires heterostructures. The morphology， structure and element composition of samples were characterized by using scanning electron microscope， transmission electron microscope， X-ray diffractometer and X-ray photoelectron spectroscopy. The results show that CuO/ZnO composite nanowires are composed of ZnO nanoparticles and CuO nanowires. Under simulated sunlight， the photocatalytic performances of the samples were studied by using Methylene Blue （MB） solution as the simulated pollutant. As a result， compared with pure CuO nanowires， CuO/ZnO composite nanowires can make the photodegradation efficiency of MB solution up to 40%， and display better photocatalytic activity. The research on photocatalytic mechanism indicates that the enhancement of the photocatalytic activity of CuO/ZnO nanocomposites is mainly due to the p-n heterojunction formed by the combination of CuO and ZnO， which effectively promotes the separation of photogenerated carriers..