The invention relates to the field of plant secondary metabolites. In order to develop a new natural anti-tumor medicine, the invention provides a diepoxy diterpene compound with an anti-tumor effectas well as a preparation method and application thereof. The chemical name of the diepoxy diterpene compound is 8(9), 12(16)-diepoxy-3, 7-dihydroxy-17 (15->16)-trans-5, 12-abietane diene-7, 11, 14-triketone. The compound is extracted and prepared from clerodendrum griffithianum, has an anti-tumor effect, has an inhibiting effect on various tumor cells such as human lung cancer cells A549, human cervical cancer HeLa cells, human breast cancer Bcap37 cells and human liver cancer SMMC7721 cells, especially has an obvious inhibitory effect on human breast cancer Bcap37 cells, has a very large application prospect in preparation of anti-tumor drugs, and plays an important role in improving the medical and economic values of clerodendrum griffithianum and promoting development and research on the nutritional value, potential toxicity, pharmacological characteristics, chemical components and the like of clerodendrum griffithianum.