NOVELTY - Preparation of azasetron hydrochloride includes dissolving alkali in water to prepare alkali solution, adding organic solvent, stirring uniformly, reducing the temperature, adding 6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxylate, stirring, cooling, regulating pH with hydrochloric acid, filtering, drying, obtaining 6-chloro-4-methyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazin-8-carboxylic acid, adding triethyl phosphite and 2,2'-disulfide benzothiazole, adding organic solvent, room temperature stirring, cooling and dropwise adding triethylamine and organic solvent.    USE - Preparation of azasetron hydrochloride (claimed).    ADVANTAGE - The method avoids multiple steps, provides no environmental pollution and has mild reaction condition and high yield.    DETAILED DESCRIPTION - Preparation of azasetron hydrochloride comprises:    (A) dissolving alkali in water to prepare alkali solution, adding organic solvent, where volume ratio of organic solvent and water is 1:1-1:3, stirring uniformly, reducing the temperature to 20-25 degrees C, adding 6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxylate, stirring, cooling, regulating pH at 1-2 with hydrochloric acid, filtering, drying and obtaining 6-chloro-4-methyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazin-8-carboxylic acid;    (B) adding 6-chloro-4-methyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazin-8-carboxylic acid with triethyl phosphite and 2,2'-disulfide benzothiazole at 1:1-1.5:1-1.5 ratio, adding in a dry flask, adding 80-120 ml organic solvent, room temperature stirring for 1-3 hours, cooling to less than 20 degrees C, dropwise adding triethylamine and 10-20 ml organic solvent, room temperature reacting for 2-3 hours to obtain intermediate B; and    (C) mixing 3-aminoquinuclidine dihydrochloride, alkali and water, cooling to 0-20 degrees C, stirring for 20 minutes, where ratio of 3-aminoquinuclidine dihydrochloride and 6-chloro-4-methyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazin-8-carboxylic acid is 1.1:1-1.3:1, adding intermediate B, room temperature reacting for 12-16 hours, adding hydrochloric acid to adjust pH at 2-3, removing organic solvent, extracting with ethyl acetate for 3 times, collecting water phase, regulating pH at 8-9 with potassium carbonate, extracting with ethyl acetate for 3 times, combining organic phase, drying, passing through hydrochloric acid gas, stirring, separating out the solid, filtering, obtaining filter cake and recrystallizing to obtain the product.