The present invention discloses a polyvinyl chloride modifier, composition and a preparation method thereof. The composition comprises the following components by parts by weight: (a) polyvinyl chloride resin of 100 parts, and (b) a toughening modifier of 2-16 parts, the toughening modifier being rubber powder whose an elongation at break is greater than 2201% and which contains weight percentage of chlorine of 5-45 wt %. The elongation at break of the polyvinyl chloride composition of the present invention is greatly improved, and the defect of low elongations at break of polyvinyl chloride product is substantially solved accordingly, therefore, the application scope of polyvinyl chloride surely will be greatly widened.