The invention discloses a plastic additive taking talcum powder as a matrix and a preparation method of the plastic additive, and belongs to the technical field of a plastic additive. The preparationmethod comprises the following steps: pretreating aluminium magnesium hydrotalcite by using citric acid, modifying the aluminium magnesium hydrotalcite by using potassium lauryl phosphate, carrying out a reaction between 2,2'-methylene-bi(4,6-ditert butyl benzene)phosphoryl chloride and acetic acid to form laurate, adding aluminum chloride to form an enhancer main body organic aluminum phosphate,and carrying out grafting copolymerization by taking ethylene-propylene-dene monomer, methyl methacrylate and acrylonitrile as raw materials to prepare an elastic substance which is wrapped the surface of a talcum powder base material, wherein a plastic matrix molecular chain permeates into grafted copolymer particles to form swelling particles in the melting and blending process of the plastic, the two phases of the commixture can synergistically resist the action of an impact force, and the capability of dissipating impact energy is high, so that the bending modulus and the tensile strengthduring plastic filling are improved. The problems of low bending modulus and low tensile strength when the plastic is filled with the talcum powder at present are solved.