NOVELTY - Preparation of (S)-2-((S)-2-amino-propionylamino)-4-carbamoyl-butyric acid involves a) reacting (S)-2-amino-4-carbamoyl-butyric acid with 2-oxo-propionyl chloride to give (S)-4-carbamoyl-2-(2-oxo-propionylamino)-butyric acid (A1); b) reacting (S)-4-carbamoyl-2-(2-oxo-propionylamino)-butyric acid (A2) with hydroxylamine hydrochloride/O-alkyl-substituted hydroxylamine hydrochloride to give substituted (S)-4-carbamoyl-2-(2-((Z)-hydroxyimino)-propionylamino)-butyric acid compound (A3); and c) catalytic hydrogenation of (A3).    USE - For preparation of N-(2)-L-alanyl acyl-L-glutamine ((S)-2-((S)-2-amino-propionylamino)-4-carbamoyl-butyric acid) (claimed) useful for supplementing L-glutamine to human body for e.g. enhancing immunologic function, maintaining intestinal mucosal integrity and adjusting intestinal flora.    ADVANTAGE - The method is simple, the reaction condition is mild, raw material source is stable, has low cost, avoids adding expensive chiral ligands, at the same time, the operation is safe, environmentally-friendly, avoids use of dangerous reagent and solvent, and has wide industrial application prospect.    DETAILED DESCRIPTION - Preparation of N-(2)-L-alanyl acyl-L-glutamine ((S)-2-((S)-2-amino-propionylamino)-4-carbamoyl-butyric acid) involves a) reacting (S)-2-amino-4-carbamoyl-butyric acid with 2-oxo-propionyl chloride to give (S)-4-carbamoyl-2-(2-oxo-propionylamino)-butyric acid; b) reacting (S)-4-carbamoyl-2-(2-oxo-propionylamino)-butyric acid with hydroxylamine hydrochloride or O-alkyl-substituted hydroxylamine hydrochloride of formula NH2-OR to give substituted (S)-4-carbamoyl-2-(2-((Z)-hydroxyimino)-propionylamino)-butyric acid compound of formula (III); and c) catalytic hydrogenation of (III) to give ((S)-2-((S)-2-amino-propionylamino)-4-carbamoyl-butyric acid). In step (c), the reaction temperature is 0-40?o C; catalyst used is palladium-carbon (Pd-C), Pd (OH)2-C, Pd-bauxite, palladium chloride (PdCl2) or PdCl2 (PPh3)2; base used is aniline, benzylamine, tert-butylamine or cyclohexylamine; and the reaction solvent is methanol, ethanol and/or isopropanol. In step (a), the reaction is carried out aqueous solution of sodium hydroxide or potassium hydroxide, and the reaction temperature is 0-10?o C, and the pH value of the solution is adjusted with hydrochloric acid or sulfuric acid.    R=H, allyl or benzyl.