The invention discloses a medicine for treating breast cancer and a preparation method and application thereof. The medicine is prepared from the following raw materials in parts by weight: 3 to 7 parts of tea polyphenol, 7 to 15 parts of diclofenac sodium, 1 to 3 parts of folic acid and 11 to 19 parts of inositol. The preparation method comprises the following steps of mixing the tea polyphenol, the diclofenac sodium and the inositol, adding deionized water with mass equal to three times of masses of the polyphenol, the diclofenac sodium and the inositol, and treating by microwaves for 8min, so as to obtain a mixture A; mixing the mixture A and the folic acid, treating by ultrasonic waves for 20min at the temperature of 40 DEG C, and stirring at the temperature of 45 DEG C until a dry state is reached, so as to obtain the medicine. The medicine has the advantages that under the synergistic action of the raw materials, the therapy effect is obvious when the breast cancer is treated; the toxic or side effect is low, and an unexpected technical effect is obtained; the raw materials are simple, and easy to obtain, the administration dosage is little, the therapy effect is high, and any toxic or side effect is avoided; the medicine is used for treating the breast cancer, the preparation technology is simple, the cost is low, and the medicine is suitable for large-scale popularization.