NOVELTY - Preparation of chiral morpholine derivative (I) involves mixing chiral serine, alcohol and catalyst, adding alkali to obtain D-alaninol derivative (III), adding alkali, adding acetyl halide, reacting, drying to obtain N-(1-hydroxypropan-2-yl)formamide derivative (IV), adding protecting group reagent, reacting, drying to obtain N-(1-hydroxypropan-2-yl)acetamide derivative (V), adding reducing agent, reacting, drying to obtain N-(1,3-dihydroxypropan-2-yl)acetamide derivative (VI), adding alkali, reacting, drying to obtain 3-morpholinone derivative (VII), reacting, drying and purifying.    USE - Method for preparing chiral morpholine derivative (claimed).    ADVANTAGE - The method is inexpensive, environment-friendly, simple, safe and economical, and produces high purity product.    DETAILED DESCRIPTION - Preparation of chiral morpholine derivative of formula (I) comprises mixing chiral serine, alcohol and catalyst, mixing at 0-150 degrees C for 1-24 hours, adding weak alkali to obtain D-alaninol derivative of formula (III), adding alkali (A) and solvent (a), cooling, adding acetyl halide, reacting at - 78-50 degrees C for 1-24 hours, washing, with sodium chloride solution, drying organic phase to obtain N-(1-hydroxypropan-2-yl)formamide derivative of formula (IV), adding alkali (B), solvent (b) and protecting group reagent, reacting at - 20-60 degrees C for 1-24 hours, adding sodium chloride solution, extracting organic phase, drying to obtain N-(1-hydroxypropan-2-yl)acetamide derivative of formula (V), adding solvent (c) and reducing agent, reacting at - 50-100 degrees C, extracting organic phase, drying to obtain N-(1,3-dihydroxypropan-2-yl)acetamide derivative of formula (VI), adding solvent (d) and alkali (C), reacting at - 50-100 degrees C for 1-24 hours, quenching, extracting organic phase, drying to obtain 3-morpholinone derivative of formula (VII), adding solvent (e) and reducing agent, reacting at - 20-150 degrees C for 1-24 hours, quenching, extracting organic phase, drying, concentrating, adding solvent (f) and deprotection agent, reacting at - 20-150 degrees C for 1-24 hours, adjusting pH, adding base (d) and N-protecting group reagent, reacting for 1-24 hours, adding organic solvent, washing, drying and purifying. Catalyst is sulfuric acid, thionyl chloride, phosphoric acid and/or sodium hydroxide. Protecting group reagent is trimethylsilyl chloride, tert-butyldimethylchlorosilane, tert-butyldiphenylchlorosilane and/or chloromethyl methyl ether. Reducing agent is potassium borohydride, lithium borohydride, calcium borohydride, sodium borohydride, lithium aluminum hydride, sodium cyanoborohydride, diisobutylaluminum hydride and/or sodium triacetoxyborohydride. Alkali deprotection reagent is tetrabutylammonium fluoride, boron trifluoride, hydrochloric acid, sulfuric acid or potassium fluoride. N-protecting group is fluorenylmethyloxycarbonyl chloride, P-toluenesulfonyl chloride, trifluoroacetic anhydride, trityl chloride, di-tert-butyl ester, benzyl chloroformate, benzaldehyde, benzyl chloride or acetic anhydride.    R=1-8C alkyl, 1-6C alkylsulfonyl, 1-4C alkyloxycarbonyl, phenyl, phenyl-methyl-oxy-carbonyl, trityl, phenylsulfonyl, halogen, nitro, alkyl, alkoxy-substituted phenyl;    R1=ethyl, propyl, butyl, benzyl, tert-butyl, tert-pentyl;    R2=methoxy, trityl, trimethylsilyl, tert-butyldimethylsilyl or silicon tert-butyl-phenyl; and    X=Cl or Br.