Abstract: Disclosed in the present invention is a preparation method for a flame retardant and an epoxy resin composite material. The preparation method for the flame retardant includes: performing silane modification on MXene; preparing a MXene dispersion; dissolving a certain amount of phosphorus-chlorine bond-rich modifier and acid scavenger in tetrahydrofuran, and adding the mixture into the MXene dispersion after complete dissolution; dissolving a certain amount of hexachlorocyclotriphosphazene and organic amine in tetrahydrofuran, and slowly adding dropwise into the mixed solution after dissolution; after completion of the reaction, filtering to obtain the product, washing the product with tetrahydrofuran and water, respectively, multiple times, and drying the product in a vacuum oven to obtain the flame retardant. The flame retardant prepared according to the present invention achieves superior flame retardancy at a lower loading content.