The invention discloses a mifepristone derivative and application thereof. The structural formula of the mifepristone derivative is represented by a formula (I) where R is acyl or sulfonyl. The invention further relates to application of the mifepristone derivative in preparation of a medicine for treating KLF5 (Kruppel-like factor 5) regulating tumors, in particular to application in preparation of a medicine for treating the triple-negative breast cancer. The compound is simple in structure and easy to prepare, has the anti-tumor activity higher than mifepristone, is small in dosage, and can be used for preparing a tumor medicine which is used for treating the triple-negative breast cancer and is closely related to the KLF5; meanwhile, the mifepristone derivative which is researched and synthesized according to the invention and has high druggability supplies a novel solution and scheme to synthesis of other compounds of the same type.