The invention belongs to the PVC modification field, and more specifically relates to a synthetic method of a PVC modifier, the PVC modifier is characterized in that butylbenzene latex with high content of butadiene is synthesized, wherein butadiene accounts for 75-95% of total amount of butadiene, then the butylbenzene latex is taken as seed for polymerization to obtain a SBR emulsion with suitable particle size, styrene and methyl methacrylate are grafted to the butylbenzene latex by two steps, the total formula amount of styrene and a few of methyl methacrylate are added in a first step, residual methyl methacrylate is added in a second step, an anti-oxidant is added finally, then dilute sulphuric acid or dilute hydrochloric acid is performed agglomeration, and the processes of washing and drying are carried out to obtain the product. Compared with a MBS mark, the low temperature impact performance of a MBS/PVC mixture can be enhanced by more than 50% on an original base, haze is obviously reduced, the color of a sheet material is pure, and the prepared product is obviously better than the MBS resin prepared by the other technologies.