The present invention provides a base film of modified polyvinyl alcohol as well as a method for preparing the base film of modified polyvinyl alcohol and a polarizer made from the base film. The method includes steps of: (1) executing surface graft modification of nano-silicon dioxide particles with fluorinated silane to obtain a modified nano-silicon dioxide powder; (2) adding the modified nano-silicon dioxide powder obtained from the step (1) to an aqueous solution of polyvinyl alcohol polymer, in order to prepare a composite solution of polyvinyl alcohol polymer; and (3) pouring the composite solution of polyvinyl alcohol polymer prepared from the step (2) onto a surface of a casting substrate to obtain a base film of modified polyvinyl alcohol (PVA). The present invention enhances the heat and humidity resistances and the stability of the PVA base film, and improves its mechanical performance and sticking-resistance.