The invention discloses a method for improving the tensile property of a polyvinyl alcohol optical film. The method is characterized in that the optical film is obtained by casting polyvinyl alcohol water solution from a die opening of an extrusion die head to the surface of a roller, heating to evaporate water, forming and stripping the optical film after heating and water evaporating, then performing heating and drying by other rollers and winding, wherein the tensile property of the polyvinyl alcohol optical film can be improved by adjusting the opening degree of a die head lip. According to the method for improving the tensile property of the polyvinyl alcohol optical film, the opening degree of the die head lip is quantitatively set, so that the tensile property of the film can be effectively improved; and moreover, the method is low in operation difficulty and economical and feasible.