Disclosed in the present invention is a protein tyrosine phosphatase inhibitor. The preparation method therefor is: extracting the crude product from the Isaria Fumosorosea Wize solid or liquid fermentation broth using ethyl acetate, ethanol, methanol, or a mixed solvent of chloroform and methanol separating the obtained extract using column chromatography on silica gel and obtaining the target product. The inhibitor can be used to prepare pharmaceutical compositions for treating and preventing diabetes, obesity and cancers.
