To solve the problems of poor visible light response and rapid electron-hole recombination of metal-organic skeleton material UiO-66, snowflake Cu2S was used as the substrate for the defect control of UiO-66, as a result, Cu2S/defective UiO-66 composite photocatalyst with p-n heterojunction was prepared by solvothermal method. The photocatalytic reduction of Cr(VI) in K2Cr2O7 solution was investigated. The results of SEM, XRD and XPS showed that the defective UiO-66 grew uniformly on Cu2S. A tight p-n heterojunction between Cu2S and defective UiO-66 was formed, which improved the utilization rate of the material to visible light and promoted the effective separation of photogenerated electron-hole pairs. Under visible light irradiation, the reduction rate of 20 mg 28% Cu2S/defective UiO-66 composite photocatalyst (28% is loading amount of defective UiO-66, based on the mass of generated Cu2S) for 50 mL 20 mg/L K2Cr2O7 solution reached to 98.92%, as well as the reduction rate of Cr(VI) still reached 96.27% after 5 cycles. The synergistic effect of defect regulation and heterojunction construction can not only effectively solve the problem of easy agglomeration of defective UiO-66 nano-catalyst, but also improve the photocatalytic reduction performance of UiO-66.