NOVELTY - Preparation of cefmetazole sodium involves reacting 7( beta )-dichloro-acetamido-3-(1-methyl-1H-tetrazol-5-mercapto methyl)-3-cephem-4-carboxylic acid triethylamine salt (I) with triethylamine, adding organic solvent and silylation reagent, halogenating obtained intermediate, cooling, adding organic base, oxidizing halogenated intermediate, adding concentrated dimethylformamide, silylating methyl oxide intermediate, adding reaction solution to purified water, cooling, adding activated carbon, removing activated carbon by filtration and drying filtrate.    USE - Preparation of cefmetazole sodium (claimed).    ADVANTAGE - The method economically provides cefmetazole sodium having high yield and purity without polluting the environment.    DETAILED DESCRIPTION - Preparation of cefmetazole sodium involves reacting 7( beta )-dichloro-acetamido-3-(1-methyl-1H-tetrazol-5-mercapto methyl)-3-cephem-4-carboxylic acid triethylamine salt of formula (I) with triethylamine, adding 15-20 wt.% organic solvent, adding silylation reagent, reacting for 1-2 hours, obtaining silylated intermediate of formula (II), halogenating the silylated intermediate (II), cooling at -20 degrees C to 80 degrees C, adding organic base and 3-5 wt.% halogenating reagent solution, stirring the reaction for 1-4 hours, obtaining halogenated intermediate of formula (III), oxidizing halogenated intermediate (III), adding methanol solution of 15-30 wt.% oxidizing agent, stirring the reaction for 0.5-2 hours, adjusting the pH of organic acid to 5-7, concentrating under reduced pressure, adding concentrated dimethylformamide, adding ethyl acetate, obtaining methyl oxide intermediate of formula (IV), silylating intermediate (IV), adding secondary silylating agent, stirring reaction at 10-50 degrees C for 1-2 hours, adding reaction solution at 0-20 degrees C to the purified water under stirring for 1-2 hours, standing for 2-3 hours, layering, removing aqueous layer, adding activated carbon into the organic phase for 0.5-2 hours, filtering to remove activated carbon by filtration,, concentrating filtrate under reduced pressure, obtaining 7( beta )-acetamido-7( alpha )-chloro-methoxy-3-(1-methyl-1H-tetrazole-5-mercaptomethyl)-4-3-cephem carboxylic acid of formula (V), dissolving S-cyanomethyl isothiourea hydrochloride salt in 30-50 wt.% dimethylformamide solution, cooling at 0-40 degrees C, adding 15-30 wt.% methanol solution of sodium methoxide or lithium methoxide, stirring reaction for 1-2 hours, dissolving compound (V) in ethyl acetate, cooling at 0-40 degrees C, adding to the resultant Cefmetazole acid side chain solution, stirring the reaction for 1-2 hours, adding reaction solution to the purified water at 0-20 degrees C, adjusting the pH of mineral acid to 1-3, allowing to stand for 1-2 hours, performing stratification, removing aqueous phase, adding activated carbon in the organic phase for 0.5-2 hours, filtering to remove the activated carbon, concentrating filtrate under reduced pressure, dissolving product in dimethylformamide, adjusting the pH of organic base to 4-7, adding cephalosporin magnesium acid amine salt crystal, stirring to crystallize, removing filtrate after filtration, and separating out crystal for drying, obtaining cefmetazole amine salt of formula (VI), adding water and ethyl acetate to the compound (VI), cooling at 0-10 degrees C, adjusting the pH of mineral acid to 1-3, then stratifying, removing aqueous phase, washing organic phase with purified water, adding activated carbon in the organic phase for 0.5-2 hours, removing activated carbon by filtration, adjusting the pH of filtrate with an inorganic base to 6-9, adding ethyl acetate and methyl isobutyl ketone, adjusting the pH of inorganic acid to 1-3, adding cephalosporin magnesium acid crystal, stirring to crystallize, removing mother liquor by filtration after crystallization, drying precipitated crystals, obtaining Cefmetazole acid of formula (VII), adding purified water, cooling at 0-20 degrees C, adjusting the pH of inorganic base to 4-6, adding activated carbon for 0.5-2 hours, removing activated carbon by filtration, and drying filtrate.