NOVELTY - The preparation method of linezolid involves: (1) adding (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-5-hydroxymethyl-oxazolidin-2-one to dichloromethane as solvent and potassium bromide solution, cooling reaction mixture; (2) adding tetramethylpiperidine-N-oxide to resultant mixture obtained in step (1) under stirring; (3) dripping sodium hypochlorite solution to resultant mixture obtained in step (2); and (4) extracting with dichloromethane, drying organic phase over anhydrous sodium sulfate, filtering and concentrating.    USE - The method is useful for preparing linezolid (claimed).    ADVANTAGE - The method prepares linezolid under mild reaction condition with high yield in an environmentally-friendly manner.    DETAILED DESCRIPTION - The preparation method of linezolid involves: (1) adding (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-5-hydroxymethyl-oxazolidin-2-one to dichloromethane as solvent and 20 %mass potassium bromide solution, cooling reaction mixture to -5 degrees C to 5 degrees C, where the mass ratio of potassium bromide solution and (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-5-hydroxymethyl-oxazolidin-2-one is 1-10:100; (2) adding tetramethylpiperidine-N-oxide to resultant mixture obtained in step (1) under stirring, where the mass ratio of tetramethylpiperidine-N-oxide and (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-5-hydroxymethyl-oxazolidin-2-one is 0.01-0.1:100; (3) dripping 6.5 %mass sodium hypochlorite solution to resultant mixture obtained in step (2), where mass ratio of sodium hypochlorite solution and (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-5-hydroxymethyl-oxazolidin-2-one is 10-20:1; (4) extracting with dichloromethane at 0-10 degrees C for 1-3 hours after the completion of dripping, drying organic phase over anhydrous sodium sulfate, filtering and concentrating to obtain (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxazolidine-5-carbaldehyde; and (5) adding methanol as solvent to (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxazolidine-5-carbaldehyde, heating at 20-50 degrees C, dripping acetamide, where the molar ratio of acetamide and (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxazolidine-5-carbaldehyde is 1-1.5:1, carrying out the reaction by liquid chromatography, directly adding reducing agent to the reaction mixture, where the molar ratio of reducing agent and (R)-3-(3-fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxazolidine-5-carbaldehyde is 1-1.5:1, precipitating and filtering.