A series of Cu-doped ZnO (Cu-ZnO) photocatalysts have been synthesized by a simple hydrothermal method. Xray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) confirmed that Cu ions have been effectively incorporated into the ZnO lattice, and as the doped Cu amounts increased to 1.5%, the Cu2O will be formed. Under the effect of Cu ions and the Cu2O/ZnO heterojunction, the prepared 1.5% Cu-ZnO nanocomposites exhibited superior catalytic activity in photodegradation of Rhodamine B (RhB) dye under UV light irradiation. RhB could be degraded 99.9% after the irradiation time of 21 min. The photodegradation rate constant achieved 0.2429 min(-1), which was 2 times than that of pure ZnO. The results of photoluminescence (PL) and photoacoustics (PA) spectroscopy studies indicated that the recombination efficiency of photogenerated electrons and holes was decreased for 1.5% Cu-ZnO nanocomposites as compared to that of samples. The surface photovoltage (SPV) and the transient photovoltage (TPV) measurements directly demonstrated that separation efficiency was improved, and the recombination time of electrons and holes in 1.5% Cu-ZnO nanocomposites was prolonged due to the synergistic effect of the impurity level and p-n heterojunction. Finally, the possible mechanism is proposed to illuminate the photogenerated charge behavior under UV light irradiation, and the roles of doped Cu and precipitated Cu2O in the photodegradation process were discussed. This work opens a novel avenue to preparing the metal doping photocatalysts with efficiently charge separation and charge transfer.