The invention discloses a bismuth vanadate/copper vanadate composite photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalysis. The bismuth vanadate/copper vanadate composite photocatalyst is formed by in-situ growth of copper vanadate nanosheets on the surfaces of bismuth vanadate micron sheets. The preparation method comprises thefollowing steps: dispersing the bismuth vanadate micron sheets into a copper nitrate solution, dropwise adding a sodium orthovanadate solution, stirring for reaction at the temperature of 25-95 DEG C, transferring a reaction product into a high-pressure reaction kettle, and performing hydrothermal reaction at the temperature of 120-180 DEG C, thereby obtaining the bismuth vanadate/copper vanadatecomposite photocatalyst. According to the bismuth vanadate/copper vanadate composite photocatalyst, the synergistic effect of bismuth vanadate and copper vanadate is utilized, the photoresponse rangeis enlarged, and the photogenerated electron-hole recombination rate is inhibited, so that the activity of photocatalytic reduction of carbon dioxide is improved, and the composite photocatalyst hasa good application effect on catalytic reduction of carbon dioxide.