A preparation method of furosemide relates to the technical field of drug synthesis. The preparation method comprises the following steps: (1) in the presence of an organic solvent, reacting 2,4-dichloro-5-sulfonamidobenzoic acid with an alkali to obtain a reaction solution, and after post-processing to obtain 2,4-dichloro-5- Sulfonamidobenzoic acid sodium salt; (2) in the presence of an organic solvent, the 2,4-dichloro-5-sulfonamidobenzoic acid sodium salt reacts with furfuryl amine; after the reaction is complete, vacuum distillation reclaims furfuryl amine and solvent , to obtain a reaction solution, after mixing the reaction solution with isopropanol, stirring, crystallization, and filtration to obtain furosemide sodium salt; (3) dissolving the furosemide sodium salt in water, activated carbon decolorization, glacial acetic acid Acidification to obtain furosemide finished product. The method has the advantages of cheap and easy-to-obtain raw materials, low cost, less time-consuming, short reaction steps, simple operation, good product quality, high yield, recyclable solvent and low environmental pollution, etc., and is suitable for industrial production.