NOVELTY - Preparing 2-amino- Delta 2-thiazoline-4-carboxylic acid (ATC), comprises e.g. reacting methyl acrylate with chlorine in a solvent, then heating it and reacting to obtain methyl 2,3-dichloropropanoate (I), then reacting (I) with aqueous sodium hydroxide solution to obtain 2-chloro-acrylic acid (II), adding thiourea and hydrochloric acid to (II) and reacting, then depressurizing and centrifuging to remove solid waste, filtering the reaction liquid and heating, adding it into ammonia water and adjusting pH, depressurizing and concentrating it, and then crystallizing and dehydrating.    USE - ATC is useful for preparing L-cysteine by enzymatic method.    ADVANTAGE - The method: utilizes special chlorination temperature control program in the step of chlorinating methyl acrylate, and thus it improves chlorination efficiency and sequentially performs four chemical processes, which are chlorination, synthesis of 2-chloro-acrylic acid, thiourea addition and cyclization without separating the intermediate product; simplifies operation steps, reduces device investment and production cost; and reduces energy consumption in intermediate product and solvent reclaiming process.    DETAILED DESCRIPTION - Preparing 2-amino- Delta 2-thiazoline-4-carboxylic acid (ATC), comprises (i) reacting methyl acrylate with chlorine gas in a solvent at -5 to 10 degrees C, heating it to 40-50 degrees C and mixing them to perform reaction after stopping feeding of gas to obtain methyl 2,3-dichloropropanoate (I), then (ii) reacting (I) with aqueous sodium hydroxide solution at 30-40 degrees C to obtain 2-chloro-acrylic acid (II), (iii) adding thiourea and hydrochloric acid to (II) without separation, performing reaction at 75-85 degrees C, then depressurizing to evaporate water, and cooling and centrifuging to remove solid waste, then (iv) filtering the reaction liquid and heating it to 60-70 degrees C, adding it into ammonium hydroxide and adjusting pH of the reaction solution to 7.0-7.5, depressurizing and concentrating it, then cooling, crystallizing, and then centrifuging and dehydrating.