Metal–organic frameworks are recognized as promising multifunctional materials, especially metal–organic framework-based photocatalysts, which are considered to be ideal photocatalytic materials. Herein, a new type of UiO-66/MoSe₂ composite was prepared using the solvothermal method. The optimum composite was selected by adjusting the mass ratio of UiO-66 and MoSe₂. X-ray diffraction analysis showed that the mass ratio influenced the crystal plane exposure rate of the composite, which may have affected its photocatalytic performance. The composite is composed of ultra-thin flower-like MoSe₂ that wrapped around cubic UiO-66, a structure that increases the abundance of active sites for reactions and is more conducive to the separation of carriers. The photocatalytic properties of the composite were evaluated by measuring the degradation rate of Rhodamine B and the catalyst’s ability to reduce Cr(VI)-containing wastewater under visible light irradiation. Rhodamine B was decolorized completely in 120 min, and most of the Cr(VI) was reduced within 150 min. The photochemical mechanism of the complex was studied in detail. The existence of Mo⁶⁺ and oxygen vacancies, in addition to the Z-type heterojunction promote the separation of electrons and holes, which enhances the photocatalytic effect.