The invention relates to a preparation method of high-quality indapamide, in particular relates to a control method of impurity A, belonging to the field of a raw material medicine production technology. The method controls the water content of a reaction system and the anhydrous aftertreatment and uses methylene dichloride to replace tetrahydrofuran to be taken as a reaction solvent, thus not only lowering the production cost, but also reducing the amount of the impurity A

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