The invention relates to 14,15-dinor-8-labdene-7,13-dione and a preparation method thereof, and belongs to the technical field of pharmaceutical chemistry and phytochemistry. The compound is named as14,15-dinor-8-labdene-7,13-dione and expressed by a molecular formula C18H29O2; and the preparation method specifically comprises the following steps: picking lower tobacco leaves of Oriental tobaccoYNOTBS1, drying the lower tobacco leaves in a shady place and then grinding the tobacco leaves, and obtaining a raw material through a 40-mesh sieve; soaking the raw material in methanol solution for10-12 hours and obtaining an extract through repeated extraction and concentration; dissolving the extract in distilled water, then carrying out extraction with ethyl acetate, recovering the solvent,carrying out separation by means of silica gel column chromatography first and then a thin-layer chromatography silica gel plate, and finally carrying out purification with a high-performance liquid chromatograph to obtain the compound. According to the invention, the compound 14,15-dinor-8-labdene-7,13-dione is separated from Oriental tobacco YNOTBS1 for the first time, and the compound has multiple biological activities, especially good activity of resisting tobacco mosaic virus, providing an important inspiration on the use of the Oriental tobacco plant as medicinal plant resource of resisting tobacco mosaic virus; and the compound can be used for development and preparation tobacco mosaic virus resisting pesticides.