NOVELTY - An olanzapine preparation method involves reacting sulfur substituted compound (II) and fluorine substituted compound (I) in the solvent in presence of potassium fluoride at 5-120 degrees C for 1-8 hours, where the solvent is dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), followed by recycling the solvent in the filtrate, adding ethanol to crystallize and separating out sulfur substituted cyanide compound (III). Mole ratio of the sulfur substituted compound (II), the fluorine substituted compound (I) to the potassium fluoride is 1: (1.0-1.6):(1-1.6).    USE - Method for preparing olanzapine.    ADVANTAGE - The method enables reducing emission of wastes and avoiding expensive reagents and virulent heavy metal i.e. tin. The method enables preparing olanzapine with high yield, better quality, safety operation and reduced environmental pollution.    DETAILED DESCRIPTION - An olanzapine preparation method involves reacting sulfur substituted compound of formula (II) and fluorine substituted compound of formula (I) in solvent in presence of potassium fluoride at 5-120 degrees C for 1-8 hours, where the solvent is dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), followed by recycling the solvent in the filtrate, adding ethanol to crystallize and separating out the sulfur substituted cyanide compound of formula (III). Mole ratio of the sulfur substituted compound of formula (II), the fluorine substituted compound of formula I to the potassium fluoride is 1: (1.0-1.6): (1-1.6). The sulfur substituted cyanide compound of formula (III) is reacted in the solvent at 10-85 degrees C with zinc powder, where the mol ratio of the sulfur substituted cyanide compound of formula (III) to the zinc powder is 1: 1-3, followed by cooling and adding sulfuric acid in the container to obtain sulfur substituted methyl compound of formula (IV). The mol ratio of the compound of formula III to the sulfuric acid is 1: (1.5-4). The obtained sulfur substituted methyl compound of formula (IV), is reacted in presence of N-methylpiperazine at 60-140 degrees C for 5-16 hours, followed by cooling and decompressing N-methylpiperazine. The distilled water is added to separate out the material, followed by cooling, filtering and drying to obtain rough product of nitrogen substituted methyl compound of formula (V)..