The present invention relates to a preparation method of an acryl-based impact-reinforcement, and more particularly, to a preparation method of an acryl-based reinforcement prepared by blending latex having large particles and latex having small particles, being capable of enhancing impact-resistance of a polyvinyl chloride (PVC) resin. The present invention provides a method of preparing an acryl-based impact reinforcement comprising a step of blending a) 50 to 90 parts by weight of latex having large particles with a particle size of 200 to 500 nm and a core-shell structure and b) 10 to 50 parts by weight of latex having small particles with a particle size of 60 to 140 nm and a core-shell structure. In addition, the present invention provides an impact-reinforcement prepared by the method of the present invention, and a polyvinyl chloride (PVC) composition comprising the same.