The invention discloses a method for preparing triptonide. Structures of the triptonide, triptolide, tripdiolide and 2-epitripdiolide existed in common caulis tripterygii wilfordii are close, whereinthe tripdiolide and the 2-epitripdiolide are a pair of chiral isomers with big separating difficulty. The four compounds are separated by depending on repeated silica column chromatography in the prior art, while repeated silica column chromatography consumes solvent, is poor in reproducibility, only suitable for less separation in experiments, and hard to popularize in industrial production. In current industrial production, only used column chromatography is a macroporous resin. The method provided by the invention can be used for separating and preparing the triptonide, the triptolide, thetripdiolide and the 2-epitripdiolide without depending on repeated silica column chromatography. The HPLC (Hight Performance Liquid Chromatography) method provided by the invention can be used for effectively separating the chiral isomers i.e. the tripdiolide and the 2-epitripdiolide based on a conventional C18 chromatographic column, and is low in cost and high in repeatability.