The invention discloses Desertorin B, and an extraction method and application thereof. The molecular formula of the Desertorin B is C25H20O8. The extraction method is as the follows: (1) carrying outstrain cultivation on decaisnea insignis endophytic fungi aspergillus tubingensis DS37, (2) carrying out fermentation cultivation on the strain obtained in the step (1) in a fermentation culture medium, then carrying out extraction with petroleum ether, ethyl acetate and methanol for a plurality of times, mixing the extracting solutions, carrying out filtering, recovering the mixed solvent, carrying out reduced pressure concentration on the filtrate to obtain a crude extract, and finally carrying out silica gel column chromatography to obtain the Desertorin B. The Desertorin B prepared by themethod has a good effect of inhibiting setosphaeria turcica, and can be used for the technologies of agricultural prevention and control and chemical prevention and control. In addition, the Desertorin B has strong activity for resisting MCF-7 and HepG2 cell lines, and can provide a possibility for the development of anti-tumor medicines. At the same time, the Desertorin B has certain antioxidantactivity.