The invention relates to the field of biological medicines, in particular to interference RNA for inhibiting the Rac1 expression and an application thereof in increasing the chemosensitivity to breastcancer, and also discloses a breast cancer chemotherapeutic drug. The invention comprises the interference RNA for inhibiting the Rac1 expression and the chemotherapeutic drug, and a carrier of tumormicroenvironment response for transporting the interference RNA and the chemotherapeutic drug. According to the invention, an acid-sensitive nano-material is used as the carrier, can efficiently convey the siRNA and the chemotherapeutic drug into tumor cells, has a long circulation time in blood, and has high enrichment amount in tumors. Meanwhile, the nano-material encapsulates the siRNA and thechemotherapeutic pro-drug, can effectively silence the target gene and effectively inhibit the expression of drug-resistant genes, enhances the killing effect on tumor cells at the same time, obviously improves the tumor chemotherapy effect, has small toxic and side effects on normal tissue cells, and has no obvious damage to important organs such as heart and liver.