The present invention discloses a method for manufacturing polarizing plates. The method comprises the following steps: providing a polyvinyl alcohol (PVA) thin film; dyeing the PVA thin film with dye and using ultraviolet irradiation to assist in dyeing for ranging the dye molecules more straightly in the polyvinyl alcohol (PVA) molecular chain; dyeing the PVA thin film with iodine solution; and forming a protective layer on the upper surface and the lower surface of the PVA thin film respectively, thus the process of manufacturing the polarizing plates is completed.