NOVELTY - Methyl-(R)-2-halo-butyrate (III) is dissolved in alcohol solvent, cooled, and processed. The mixture is heated, concentrated, precipitated, filtration and dried, to obtain (S)-2-aminobutanamide hydrochloride (IV). The filtrate is diluted with organic solvent. Chlorinated paraffin and solvent (s1) are added to (S)-2-aminobutanamide hydrochloride (IV). Base and phase transfer catalyst are added to mixture and stirred, and 4-chlorobutanoyl chloride (V) and 4-chlorobutyryl chloride are added to mixture, heated, filtered and distilled, to obtain levetiracetam (I).    USE - Preparation of levetiracetam (claimed).    ADVANTAGE - The method enables preparation of levetiracetam with high yield by economical and environmentally-friendly method using bioenzyme catalyst having high enantioselectivity and regioselectivity, within short period of time and with low energy consumption and byproduct and waste discharge.    DETAILED DESCRIPTION - A phosphate buffer solution with pH value of 6.5-7.5, racemic methyl-2-halo-butyrate of formula (II) and lipase are reacted at 20-40 degrees C for 12-72 hours. The reaction mixture is extracted with ethyl acetate, and organic layer is collected and spin-dried, to obtain methyl-(R)-2-halo-butyrate of formula (III). The lipase comprises immobilized lipase. The mass ratio of racemic methyl-2-halo-butyrate (II) and lipase is 1:0.01-0.2. Methyl-(R)-2-halo-butyrate (III) is dissolved in alcohol solvent, cooled to -10 degrees C to 0 degrees C and ammonia is added to mixture, and processed at pressure of 0.2-1 MPa. The mixture is heated at 20-60 degrees C, and completion of reaction is tracked with thin-layer chromatography. The reaction solution is concentrated under reduced pressure, and solid is precipitated and filtered. The filtrate is diluted with organic solvent, and concentrated hydrochloric acid is dripped to mixture, and pH is adjusted to 1-2. The solid is precipitated from mixture, filtration and dried, to obtain (S)-2-aminobutanamide hydrochloride of formula (IV). The solvent alcohol comprises methanol or ethanol. The filtrate is diluted with organic solvent chosen from hexane, dichloromethane, chloroform, ethyl acetate, butyl acetate, methanol, ethanol and isopropanol. Chlorinated paraffin and solvent (s1) are added to (S)-2-aminobutanamide hydrochloride (IV). Base and phase transfer catalyst are added to mixture, stirred and cooled to -10 degrees C to 0 degrees C, and 4-chlorobutanoyl chloride of formula (V) and 4-chlorobutyryl chloride are added to mixture, heated at 25-40 degrees C. The completion of reaction is tracked with thin-layer chromatography. The reaction liquid is filtered, distilled to remove solvent, and residue is recrystallized from ethyl acetate, to obtain levetiracetam ((2S)-2-(2-oxopyrrolidin-1-yl)butanamide of formula (I)). The solvent (s1) comprises methylene chloride or chloroform. The base comprises potassium hydroxide or sodium hydroxide. The phase transfer catalyst comprises 4-butylammonium bromide. The weight ratio of (S)-2-aminobutanamide hydrochloride, 4-chlorobutyryl chloride and base is 1:3-5:1-2. The usage amount of phase transfer catalyst is 1-10 %mass of (S)-2-aminobutanamide hydrochloride.    X=bromo or chloro.