By means of that the glucose radical on ginsenoside 20-hydroxyl radical has lower stability than glucose radical on ginsenoside 3-hydroxyl radical in acid environment and that the 20-hydroxyl radical may be dewatered to become double bonds in acid condition, the present invention solves the problems of directional hydrolysis of ginsenoside in acid hydrolysis condition through adding protecting agent and protective inert gas, controlling reaction temperature and acid concentration and other measures, so as to acid hydrolyze ginsenoside directly to prepare Rk1 and Rg5. The said process is simple, convenient and low in cost, and makes it possible to prepare Rk1 and Rg5 in large scale for preparing antitumor medicine. |