The invention belongs to the field of 
photocatalysis, and particularly relates to a BiVO4 / BiOI 
heterojunction compound photocatalyst and a preparation method and application thereof. The BiVO4 / BiOI 
heterojunction compound photocatalyst is composed of BiVO4 and BiOI, wherein the 
mole ratio of BiVO4 to BiOI is 1:99-99:1. In preparation, BiOI of a three-dimensional layering 
microsphere structure is first prepared through a 
hydrothermal synthesis method, and then through an 
ion exchange method, the BiVO4 / BiOI 
heterojunction compound photocatalyst is obtained under a hydrothermal condition. The preparation method is simple in technology, easy to control and low in cost; the BiVO4 / BiOI heterojunction structure with visible-
light response is constructed, and the BiVO4 / BiOI heterojunction compound photocatalyst accelerates separation of 
photon-generated vectors, lowers the compound probability of photo-induced 
electron-hole pairs, has efficient photocatalytic activity and stability under visible light, efficiently kills and degrades harmful microorganisms and dye contaminants in a 
water body, and has quite high practical value and potential application prospects in the fields of 
water body purifying, ocean antifouling and others.