The invention relates to a usage of an ocean fungal extract-active natural product B. According to the result of an in vitro research trial, the active natural product B has certain inhibitory effecton common clinical pathogenic fungi such as white tritirachium album limber, cryptococcus neoformans, trichophyton rubrum and aspergillus fumigatus and the like, is able to inordinately inhibit the growth of tumor cell lines such as liver cancer, breast cancer and lung cancer and the like, and is able to have stronger protective effect on pathological mechanism damages caused by rat multi-infarctcerebral ischemia damage and the like, thus being capable of obviously improving the learning and memory functions of dementia rat, and being applied to prepare dementia product having anti-angiogeniceffect. The invention provides a new pharmaceutical source for the curing of clinical antifungal, antitumor and anti-vascular dementia and directly related diseases thereof, having important value for developing and utilizing the pharmaceutical resource of our country.