The invention relates to a method for preparing a jatrophane diterpene compound. The three-dimensional liquid-phase chromatographic technology is adopted. Firstly, hexane-ethanol serves as a mobile phase, a normal-phase silicagel chromatographic column serves as a one-dimensional prepared chromatographic column, a kansui root extract is subjected to component cutting, and a target component is collected to serve as a one-dimensional separated component; secondly, water-acetonitrile serves as a mobile phase, a C18(250mm*20mm) chromatographic column serves as a two-dimensional prepared chromatographic column, the one-dimensional separated component is subjected to component cutting, collection, rotary evaporation and concentration, and a two-dimensional separated component is obtained; finally, a C18(250mm*10mm) chromatographic column serves as a three-dimensional prepared chromatographic column, high-purity kansuininA is obtained, and the purity can reach over 98%. The preparation process is high in repeatability, and operability is good; meanwhile, kansui root resources are rich, easy to obtain and suitable for meeting the requirement of large-scale production.