A method for preparing highly purified glatiramer acetate, comprising the following steps: 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, and stirring until a clarified solution is formed; adding diethylamine for catalysis, stirring at 20-25°C, then slowly pouring the reaction solution into water, collecting the produced white fully protected solid glatiramer, and drying it; providing a solution of hydrobromic acid in acetic acid, said hydrobromic acid comprising a proportion of bromine in the form of the elementary substance and said solution further comprising an amount of phenol; placing the solution of step into a reactor, then adding the fully protected glatiramer obtained in step to the reactor, stirring at 23.0-25.0°C, pouring the reaction solution into purified water for quenching when the reaction is over, stirring for 5 minutes, subjecting the mixture to suction filtration to obtain a yellow powdery solid trifluoroacetyl glatiramer, after repeating the steps of dissolving in water, suction filtration and drying 3-5 times, subjecting the solid trifluoroacetyl glatiramer to blast drying to remove the moisture therein; and dissolving the trifluoroacetyl glatiramer obtained in step 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 obtaining white powdery glatiramer acetate after lyophilisation, characterized in that (i) in step the proportion of bromine in the form of elementary substance in the solution of hydrobromic acid in acetic acid ranges from 0.7 to 1 wt.-%, (ii) the solution of hydrobromic acid in acetic acid further contains 0.5 to 1.0 wt.-% of phenol, and (iii) stirring the solution of hydrobromic acid for a period of about 30 minutes. 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, and stirring until a clarified solution is formed; adding diethylamine for catalysis, stirring at 20-25°C, then slowly pouring the reaction solution into water, collecting the produced white fully protected solid glatiramer, and drying it; providing a solution of hydrobromic acid in acetic acid, said hydrobromic acid comprising a proportion of bromine in the form of the elementary substance and said solution further comprising an amount of phenol; placing the solution of step into a reactor, then adding the fully protected glatiramer obtained in step to the reactor, stirring at 23.0-25.0°C, pouring the reaction solution into purified water for quenching when the reaction is over, stirring for 5 minutes, subjecting the mixture to suction filtration to obtain a yellow powdery solid trifluoroacetyl glatiramer, after repeating the steps of dissolving in water, suction filtration and drying 3-5 times, subjecting the solid trifluoroacetyl glatiramer to blast drying to remove the moisture therein; and dissolving the trifluoroacetyl glatiramer obtained in step 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 obtaining white powdery glatiramer acetate after lyophilisation, (i) in step the proportion of bromine in the form of elementary substance in the solution of hydrobromic acid in acetic acid ranges from 0.7 to 1 wt.-%, (ii) the solution of hydrobromic acid in acetic acid further contains 0.5 to 1.0 wt.-% of phenol, and (iii) stirring the solution of hydrobromic acid for a period of about 30 minutes.