Preparation method for (S)-methyldopa intermediate compound

The invention discloses a preparation method for a (S)-methyldopa intermediate compound shown as formula (II). The method comprises the steps of: in the presence of inorganic acid, subjecting the compound shown as formula (I) and (2S, 3S)-tartaric acid to salt forming reaction as shown below in water, with the mole ratio of the (2S, 3S)-tartaric acid to the compound shown as formula (I) being 0.5:1-0.6:1. The preparation method provided by the invention employs (2S, 3S)-tartaric acid as the resolving agent, which has the characteristics of high-usage, high optical purity, simple operation and low cost. (salt forming reaction).