The invention discloses a preparation method of R-lipoic acid tromethamine salt and belongs to the field of organic medicinal chemistry. The method includes the steps that (S)-6,8-dichloro ethyl caprylate and sulphur are put into a reaction vessel, the temperature is raised, a cyclization reaction is carried out, the temperature is preserved, extraction is carried out with a first organic solvent, concentration is carried out, and cyclization liquid is obtained; then, a hydrolysis reaction is carried out, cooling is carried out, and hydrolysis liquid is obtained; a second organic solvent is added into the hydrolysis liquid, the pH value is regulated, extraction is carried out, an obtained organic layer is washed with water to be neutral, the second organic solvent is removed at reduced pressure, and an initial product is obtained; mixed liquor is added into the initial product, the temperature is raised, a first filter aid is added, stirring adsorption is carried out, filtration is carried out, and light yellow liquid is obtained; cooling is carried out to separate out crystals, and R-lipoic acid is obtained; R-lipoic acid is dissolved, trihydroxymethyl aminomethane is added, the temperature is raised for solution, a second filter aid is added for filtration, and light yellow liquid is obtained; cooling is carried out to separate out crystals, centrifugal drying is carried out, and the finished product is obtained. According to the method, few steps are needed, efficiency is high, energy is saved, and waste discharge is reduced.