The present invention relates to the field of medicinal chemistry, and specifically to a sweet potato sitosterol glycoside unsaturated fatty acid, an extract, a preparation method therefor, and an application thereof. Sweet potato sitosterol glycoside linolenic acid ester has a significant effect on inhibiting the growth of tumor cells. In the case of an administration concentration of 10 mg/L, the inhibition rate of a sweet potato sitosterol glycoside linolenic acid ester monomer of the present invention on MCF-7 cells is 92%, the inhibition rate of a sweet potato sitosterol glycoside linoleic acid ester monomer on MCF-7 cells is 65%, and the inhibition rate of a sweet potato sitosterol glycoside monomer on MCF-7 cells is 55%; in the case of an administration concentration of 1 mg/L, the inhibition rate of a contrastive sweet potato sitosterol glycoside linolenic acid ester monomer on MCF-7 cells is 45%, the inhibition rate of a sweet potato sitosterol glycoside linoleic acid ester monomer on MCF-7 cells is 15%, and the inhibition rate of a contrastive drug, i.e., a sweet potato sitosterol glycoside monomer on MCF-7 cells is 10%.