The present invention discloses a method for preparing glatiramer acetate, comprising: (1) dissolving L-alanine NCA, L-tyrosine NCA, L-glutamic acid-γ-benzyl ester NCA, and L-ε-trifluoroacetyl-lysine NCA in 1,4-dioxane as solvent, stirring until a clarified solution is formed; (2) adding diethylamine for catalysis, stirring at 20-25° C., then slowly pouring the reaction solution into water, collecting the produced white product; (3) adding the obtained product to a solution of hydrobromic acid in acetic acid, stirring at 23.0-25.0° C., pouring the reaction solution into purified water for quenching and stirring, subjecting the mixture to suction filtration to obtain a yellow solid, after repeating 3-5 times, subjecting the solid to blast drying to remove the moisture therein; and (4) dissolving the solid obtained in step (3) in a 1M piperidine aqueous solution at room temperature and stirring, subjecting the obtained solution to dialysis, adding glacial acetic acid to adjust the pH to 5.5-7.0, and lyophilizing.