The invention discloses a preparation method of a flower shaped ZnO/graphene composite microsphere. The preparation method comprises the following steps: mixing zinc acetate and critic acid, sequentially adding deionized water and anhydrous ethanol into the mixture, evenly mixing, slowly adding sodium hydroxide; transferring the solution to a reactor, drying the reactor, naturally cooling to the room temperature, washing the reaction product by deionized water and anhydrous ethanol, drying the obtained sample overnight in vacuum; transferring the solution to a reactor, drying the reactor, naturally cooling to the room temperature, washing the reaction product by deionized water and anhydrous ethanol, and drying the obtained sample overnight in vacuum. By combining ZnO and graphene, the separation of electron and cavity is promoted, the combination of electron and cavity is inhibited, thus a photocatalyst material having the advantages of high catalytic efficiency and low cost can be obtained, and under the irritation of ultraviolet rays, the methyl orange can be degraded in the presence of the flower shaped ZnO/graphene composite microsphere. Through the graphene doping, the transferring of photo-generated electron is promoted, the electron-cavity combination is inhibited, and thus the photocatalytic performance is enhanced.