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Step I, preparation of Vilmerier reagent: 71.4 g (0.6 mol) of thionyl chloride was added to a 250 mL four-necked flask, cooled to 5~10°C in an ice-water bath, and 50.4 g (0.69 mol) of dry N,N-dimethylformamide was slowly added, the reaction was exothermic obviously, and mechanically stirred for 2 h to obtain a colorless Vilmerier reagent solution. Step II, Synthesis of methyl (S)-2-chloropropionate: a small amount of dioxane was added to the Vilmerier reagent solution obtained in Step I via a constant pressure dropping funnel at 20~30°C to form a mixed solution. Subsequently, 62.4 g (0.6 mol) of (R)-lactic acid methyl ester was slowly added dropwise to the mixed solution, and the reaction was markedly exothermic and gas was generated. After the dropwise addition, the reaction was continued with stirring and heated to 55°C for 6 h to obtain a solution of methyl (S)-2-chloropropionate. After the reaction was completed, the reaction mixture was cooled. Step III, post-treatment: the (S)-2-chloropropionic acid methyl ester solution obtained in Step II was washed, desolventized and distilled to obtain the product (S)-2-chloropropionic acid methyl ester 54.4 g, with 86% yield and 87% optical purity.