Abstract: Natural compound osthol has been proved to have a wide spectrum of fungi inhibition including Rhizoctonia solani, Colletotrichum musae, Rhizoctonia solani , Phytophora capsici, Collectotrum gloesporioides, Botrytis cinerea Pers, Sclerotinia sclerotiorum, Fusarium graminearum, Macrophoma kawatsukai, with the value of EC50 ranged from 21.15 μg/mL to 61.62 μg/mL to some fungi. F. graminearuym was used to research the inhibition mechanism of osthol, the results showed 50 μg/mL osthol could inhibit the germination of its spores evidently. After treatment of osthol for 24 h, the hyphae of this fungus growing in aliqousculture came into large mounts of fragments. Glucose content decreased firstly and then increased to the level of control. Soluble proteins, chitin content and chitinase activity were higher than that of control.