The invention discloses a method for preparing polyglutamic acid hydrogel. In the method, polyglutamic acid is used as a main raw material, glycol diglycidyl ether is used as a crosslinking agent and a pH value of the system is adjusted at regular intervals in the reaction process. The method comprises the following steps of: dissolving 15 to 30 percent of polyglutamic acid into distilled water, adding glycol diglycidyl ether in an amount which is 20 to 50 percent based on the molar amount of of polyglutamic acid monomers, uniformly stirring the mixed solution, adjusting the pH value of the system to 3 to 5, and performing a reaction at the temperature of between 40 and 80 DEG C for 4 to 10 hours, wherein the pH value of the system is adjusted to the initial value every 1 to 2 hours; and performing full swelling dialysis and drying of the prepared hydrogel. The method has the advantages that: the reaction is performed in aqueous solution, which contributes to environmental protection;and the preparation period is short, and the hydrogel prepared by the method is high in water absorption and high in swelling speed, and possesses bio-degradability. The hydrogel prepared by the method can be applied to medicament carriers, medical and hygienic products, water-retaining agents used in farming, forestry and gardening industries, thickening agents for cosmetics and foods, anti-condensation agents, flocculating agents, water treatment chemicals and the like.