The invention discloses a preparation method and application of flower-like BiOBr, belonging to the field of photocatalysts. The BiOBr has flower-like structure, and has favorable dispersity; and the petal thickness is 20-40nm, and the corolla diameter is 1-1.5 mu m. The preparation method comprises the following steps: measuring toluene, putting the toluene into a round-bottom flask, stirring at constant temperature, adding cetyl trimethylammonium bromide and oleic acid, and stirring for dissolution to obtain a solution A; measuring a certain amount of water, and adding HNO3 and Bi(NO3)3.5H2O to obtain a solution B; and while stirring, dropwisely adding the solution B into the solution A, continuing stirring for 12 hours, heating to 85 DEG C, refluxing for 12 hours, cooling the reaction product, separating, washing, and drying to obtain the flower-like BiOBr. The flower-like BiOBr can be used as a photocatalyst for degrading the organic pollutant rhodamine in water, and has favorable catalytic effect and high stability.