The invention discloses a BiOI/BiOBr multilevel structure composite visible light catalyst, and a preparation method and application thereof, and belongs to the field of the water treatment of photocatalytic materials. The composite photochemical catalyst BiOI/BiOBr which has a special appearance and a high catalytic effect is prepared by a low-temperature substep precipitation method. A BiOI/BiOBr composite is compounded by two different band gap semiconductor effective bodies, the light absorption range is expanded, the separation of photon-generated carriers is accelerated, and the compounding of electron hole pairs is reduced, so that the photocatalytic activity of light materials is improved. The method is easy to operate and low in cost, and a structure and composition of a photocatalytic composite material can be controlled effectively to control the photo-electrochemical property of the photocatalytic composite material, so that the BiOI/BiOBr multilevel structure composite visible light catalyst has the significant application value on the preparation of the semiconductor composite material.