The invention relates to a compound extracted from isodon excisoides and a preparation method and application of the compound, and aims to effectively solve the problem of preparation of maceryatal B homolog in isodon excisoides. According to the technical scheme, the compound is white crystal, the molecular weight of the compound is 394, the molecular formula of the compound is C22H34O6, the unsaturation degree is 6, the structure is 1 alpha-acetyl-7 alpha, 14 beta, 20 alpha-trihydroxy-ent-kaurane-16-alkene-15-ketone, and the compound is a diterpene compound and is named as Excisoides D; the preparation method of the compound comprises the following steps: drying ground parts of the isodon excisoides, crushing, boiling with water for extraction, and extracting and purifying by using a macroreticular resin column, gel column chromatography, a Sephadex LH-20 column and semi-preparative HPLC (High Performance Liquid Chromatography), thereby obtaining the compound. The compound has an anti-tumor function, is easy to operate, high in separation speed, high in product purity and remarkable in economic and social benefit, and medicinal values of the isodon excisoides are developed.