The surface of ZnWO4 nanorods was decorated with Cu2O nanoparticles (Cu2O/ZnWO4) prepared through a precipitation method. The Cu2O nanoparticles were tightly deposited on the ZnWO4 surface and had average diameters of 20 nm. The nanoparticles not only promoted the absorption and utilization of visible light but also facilitated the separation of photogenerated charge carriers. This brought an improvement of the photocatalytic activity. The 5 wt % Cu2O/ZnWO4 photocatalyst displayed the highest degrade efficiency for methylene blue (MB) degradation under visible light, which was 7.8 and 2 times higher than pure ZnWO4 and Cu2O, respectively. Meanwhile, the Cu2O/ZnWO4 composite photocatalyst was able to go through phenol degradation under visible light. The results of photoluminescence (PL), photocurrent, and electrochemical impedance spectra (EIS) measurements were consistent and prove the rapid separation of charge, which originated from the match level structure and the close contact with the interface. The radical and hole trapping experiments were carried out to detect the main active substances in the photodegradation process. The holes and ·O2− radicals were predicted to dominate the photocatalytic process. Based on the characterization analysis and experiment results, a possible photocatalytic mechanism for enhancing photocatalytic activity was proposed.