The invention discloses an 
ursodesoxycholic acid preparation method. The method comprises the following steps: 1, adding 
chenodeoxycholic acid and a 
solvent A to a reaction container, stirring for dissolving, adding 7-alphaHSDH, 7-betaHSDH and a coenzyme II, and carrying out a reaction at a controlled temperature at a controlled pH value to convert 
chenodeoxycholic acid into 
ursodesoxycholic acid in order to obtain a conversion liquid; 2, heating the conversion liquid obtained in step 1 to denaturalize the 7-alphaHSDH and the 7-betaHSDH, centrifuging through a high speed 
centrifuge, removing proteins, adding a 
sodium hydroxide solution to the above obtained solution, distilling to remove the 
solvent A, adding water to dissolve obtained 
distillation residues, adding an acid, and crystallizing to obtain crude 
ursodesoxycholic acid; and 3, adding the crude ursodesoxycholic acid obtained in step 2 and a 
solvent B to the reaction container, heating and refluxing the crude ursodesoxycholic acid and the solvent B for 1h, cooling the obtained 
reaction product to normal temperature, and filtering the cooled product to obtain ursodesoxycholic acid with the purity being greater than 99%. The ursodesoxycholic acid preparation method has the advantages of simple technology, short synthesis 
route, high conversion rate, easy post-treatment and 
environmental protection.