Photocatalytic conversion of CO₂ into renewable hydrocarbons using solar energy is one of the potential solutions to both global warming and fuel crisis. Of particular interest in this work, we prepared AgI/Ag₃PO₄ heterojunction catalyst as photocatalyst to convert CO₂ into value-added products. The synthesis route of AgI/Ag₃PO₄ involved first ion-exchange preparation of tetrahedron Ag₃PO₄ followed by precipitation of AgI. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area test (BET), and ultraviolet-visible absorption spectra (UV-Vis). With the mole ratio of AgI/Ag₃PO₄ being 30%, the catalyst showed the best catalytic performance for reduction of CO₂, and the major product was CH₄. The pronounced photocatalytic performance should be attributed to the efficient separation of the light electrons and holes arisen from the p-n junction between Ag₃PO₄ and AgI.