NOVELTY - Preparing tenatoprazole, comprises e.g. blending 2-mercapto-5-methoxy imidazo(4,5-b)pyridine (I), an inorganic alkali and water, and performing condensation reaction with aqueous solution of 2-chloromethyl-3,5-dimethyl-4-methoxy-pyridine hydrochloride (II) to obtain 5-methoxy-2-((4-methoxy-3,5-dimethylpyridin-2-yl)methylthio)-3H-imidazo(4,5-b)pyridine (III), then blending (III), dichloromethane and methanol and oxidizing with dichloromethane solution of meta-chloroperoxybenzoic acid to obtain tenatoprazole salt, and then reacting tenatoprazole salt with a hydrophilic solvent and water.    USE - The method is useful for preparing tenatoprazole.    ADVANTAGE - The method: utilizes water as solvent for condensation reaction instead of ethanol or methanol, and thus it reduces solvent distilling and recycling, chloroform extracting and solvent crystallizing steps; does not uses toxic and hazardous solvents; performs condensation reaction at normal temperature, utilizes mixed solvent of methanol and dichloromethane for oxidizing reaction instead of chloroform having higher hepatotoxicity; and recycles residual solvent.    DETAILED DESCRIPTION - Preparing tenatoprazole, comprises (i) adding 2-mercapto-5-methoxy imidazo(4,5-b)pyridine (I), an inorganic alkali and water into a reaction bottle, and blending them and dissolving, then adding aqueous solution of 2-chloromethyl-3,5-dimethyl-4-methoxy-pyridine hydrochloride (20-25%) (II) for 1-2 hours and performing condensation reaction for 2-4 hours at normal temperature, filtering the reaction mixture, washing and drying to obtain 5-Methoxy-2-((4-methoxy-3,5-dimethylpyridin-2-yl)methylthio)-3H-imidazo(4,5-b)pyridine (III), where molar ratio between (I) and the inorganic alkali is 1:2-3, weight ratio between (I) and water is 1:8-12, and molar ratio between (I) and (II) is 1:0.9-1.5, then (ii) adding (III), dichloromethane and methanol into a reaction bottle, blending and dissolving them, then cooling to -10 to -20 degrees C, adding dichloromethane solution of meta-chloroperoxybenzoic acid (3-6%) at -10 to -20 degrees C for 2-3 hours, and oxidizing at -10 to -20 degrees C for 30-40 minutes, then adding aqueous solution of inorganic alkali (10-20%) at 10-20 degrees C and blending for 1-2 hours, filtering the blended mixture, washing and drying to obtain tenatoprazole salt, where weight ratio between (III) and dichloromethane is 1:0.5-2, weight ratio between (III) and meta-chloroperoxybenzoic acid is 1:0.5-0.6, and weight ratio between (III) and the inorganic alkali is 1:0.5-1, and (iii) adding tenatoprazole salt, a hydrophilic solvent and water into a reaction bottle, cooling to 0-10 degrees C, then adding 1-6 mol/l of hydrochloric acid for 1-2 hours to adjust pH to 7-8, filtering the reaction mixture, washing and drying, where weight ratio between tenatoprazole salt, hydrophilic solvent and water is 1:2-3:4-6.