This invention relates to the compound extracted from husk and fruit stem of Xanthoceras Sobifolia and its extracting method and use thereof. Its chemical structure is as below: A method on its extraction: grinding the husk and fruit stem of Xanthoceras Sobifolia into particles, extracting the particles with solvents, filtrating, reclaiming the solvent and collecting the concentrated solution, passing the collection through macroporous resin, eluting it by solvent, reclaiming the solvent to get the enriched solution, drying the solution to form a brown solid which called total saponins; then dissolving the total saponins in water, extracting by normal butyl alcohol, having the extraction dried to obtain brown powder, chromatographing the powder resolved solution by silica gel column repeatedly, receipting the gradient elution with 100:(35˜60) chloroform:methanol, reclaiming the eluted solution, refining and re-crystallize the left solution, will obtain the white raphide which is the invention compound—Xanthoceraside. It is verified that the compound can be used to make medicine to treat brain diseases and tumors, and to make health food to prevent and cure brain diseases and tumors.