NOVELTY - Preparation of L-methionine involves: (1) dissolving amino-acylase in acetyl-DL-methionine aqueous solution, regulating the pH, decompressing condensing, cooling and filtering to obtain L-methionine crystals and mother liquor containing acetyl-D-methionine; (2) adding sodium hydroxide aqueous solution into the mother liquor, racemizing and decompressing condensing; (3) cooling the racemic liquid, separating crystals and filtering to obtain sodium acetate trihydrate crystals and concentrated solution and (4) adding acetic anhydride to the concentrated solution and acylating.    USE - Preparation of L-methionine (claimed).    ADVANTAGE - The method allows recycling of acetyl-DLmethionineen in an economic and environmentally sustainable manner.    DETAILED DESCRIPTION - Preparation of L-methionine comprises:    (1) dissolving amino-acylase into acetyl-DL-methionine aqueous solution, regulating the pH of the obtained reaction liquid to neutral, resolving at 35-45 degrees C, decompressing condensing, cooling to separate crystals, and filtering to obtain L-methionine crystals and mother liquor containing acetyl-D-methionine;    (2) adding sodium hydroxide aqueous solution with a concentration of 25-30% into the mother liquor and racemizing at pH 12-14 and 100-110 degrees C, maintaining the temperature, decompressing condensing so that the water content removed is not less than the water content of the sodium hydroxide aqueous solution to obtain racemic liquid;    (3) cooling the racemic liquid to 50-55 degrees C, adjusting the pH of the solution to 8.8- 9.2 with acetic acid, separating a large quantity of crystals and filtering to obtain sodium acetate trihydrate crystals and concentrated solution, and    (4) adding acetic anhydride into the concentrated solution and acylating at 50-55 degrees C, cooling to room temperature, separating a large quantity of crystals and centrifuging to obtain trihydrate sodium acetate crystals and mother liquor containing acetyl-DLmethionine used as the acetyl-DL-methionine aqueous solution in step (1).