The invention belongs to the technical field of inorganic chemicals and in particular relates to a method for preparing an aluminum triphosphate-based composite preservative pigment. According to the method, a superfine aluminum triphosphate-based composite preservative pigment is prepared by using a one-step synthesis method, modification and secondary crushing are completed at one step, the corrosion resistance of a material is greatly improved, preparation processes are simplified, the energy is saved, the production cost is reduced, in addition, no industrial pollution such as wastewater and waste residues is generated in the production process, and thus the method belongs to the field of green chemistry.