NOVELTY - Preparing linezolid involves reacting (S)-N-(((3-(3-fluoro-4-morpholinyl)phenyl)-2-oxo-5-oxazolidinyl)methyl)phthalimide and hydrazine hydrate using methanol as solvent, heating and reacting completely, then to reaction solution, adding water and methylene dichloride completely, combining organic layer and concentrating, concentrating reaction solution in toluene, then adding acetic anhydride, after reacting completely, cooling, stirring, separating out crystal, filtering product, when reaction is complete filtering liquid to remove solid, separating the filtrate and concentrating.    USE - For the preparation of linezolid (claimed) used for the treatment of infection caused by aerobic gram positive bacteria, some gram-negative bacteria and anaerobic bacteria.    ADVANTAGE - Compared with the existing technology, the method provides product with high purity, in high yield, greatly reduces cost, allows large scale industrial production of linezolid and at the same time, is environment-friendly. The method provides product in more than 80% yield, and with more than 90% purity.    DETAILED DESCRIPTION - Preparation of linezolid involves reacting (S)-N-(((3-(3-fluoro-4-morpholinyl)phenyl)-2-oxo-5-oxazolidinyl)methyl)phthalimide and hydrazine hydrate raw materials using methanol as solvent, heating and reacting completely, then to the reaction solution obtained, adding water and methylene dichloride completely, combining organic layer and concentrating, concentrating reaction solution in toluene, and then adding acetic anhydride, after reacting completely, cooling, stirring, separating out crystal, filtering the product, when the reaction is complete firstly filtering liquid to remove solid, separating the filtrate and concentrating. The volume mass ratio of (S)-N-(((3-(3-fluoro-4-morpholinyl)phenyl)-2-oxo-5-oxazolidinyl)methyl)phthalimide and hydrazine hydrate is greater than or equal to 3:1, preferably 5:1-50:1, especially 5:1-10:1. The toluene is added at 30 degrees C to 110 degrees C, preferably at 60 degrees C to 80 degrees C.