NOVELTY - Preparation of amoxicillin trihydrate (I) involves adding D-aspartic acid to mixed solution of thionyl chloride and methanol, reacting with methylamine alcohol solution, adding potassium hydroxide, filtering, reacting with ethyl acetoacetate (Ib), reacting the resultant product with 2-(1,3-benzothiazol-2-yldisulfanyl)-1,3-benzothiazole (Ic) in acetonitrile solvent and organic base catalyst, obtaining ethyl (3E)-3-(((2R)-1-(1,3-benzothiazol-2-ylsulfanyl)-3-(methylcarbamoyl)-1-oxopropan-2-yl)imino)butanoate (IV) and condensing with amoxicillin (Id).    USE - Preparation of amoxicillin trihydrate used in drug.    ADVANTAGE - The method enables environmentally-friendly and economical preparation of amoxicillin trihydrate purity of more than 99% and single impurity content of less than 0.2%, with high yield, using readily available raw materials, with low reaction toxicity.    DETAILED DESCRIPTION - Preparation of amoxicillin trihydrate of formula (I) involves adding D-aspartic acid of formula (Ia) to mixed solution of thionyl chloride and methanol at 0-5 degrees C, obtaining D-2-amino-3-methoxycarbonyl-propanoic acid hydrochloride of formula (II), reacting the resultant product with methylamine alcohol solution at 40 degrees C, adding potassium hydroxide, filtering the resultant product, evaporating the filtrate and remaining methylamine, adding ethanol to dissolve, reacting with ethyl acetoacetate of formula (Ib), obtaining potassium methyl (3E)-3-(((2R)-1-(methylcarbamoyl)-3-oxobutan-2-yl)imino)butanoate of formula (III), reacting the resultant product with 2-(1,3-benzothiazol-2-yldisulfanyl)-1,3-benzothiazole of formula (Ic) in acetonitrile solvent and organic base chosen from pyridine, triethylamine and N-methylmorpholine as catalyst, obtaining ethyl (3E)-3-(((2R)-1-(1,3-benzothiazol-2-ylsulfanyl)-3-(methylcarbamoyl)-1-oxopropan-2-yl)imino)butanoate of formula (IV), condensing the resultant product in triethylamine with amoxicillin of formula (Id), and obtaining white crystals of amoxicillin trihydrate.