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.