The invention discloses a preparation method of a raw material PVA for production of a polyvinyl alcohol optical film. Specifically, a quantitative plasticizer is added in a polymerization and/or alcoholysis process so as to obtain a plasticizer-containing polyvinyl alcohol product. According to the invention, the plasticizer is added in the production process of polyvinyl alcohol, and a vinyl acetate monomer or polyvinyl acetate is mixed with the plasticizer, thus avoiding the effect of macromolecular chain steric hindrance formed by hydrogen bond, and acquiring a better mixing effect. Compared with a polyvinyl alcohol optical film with a same plasticizer content in a solution blending process, the polyvinyl alcohol optical film prepared from the raw material PVA according to the invention has a better stretching ratio.