Adjuvant chemotherapy applied after surgery for invasive breast cancer can improve survival. Breast cancer is one of the most effective tumors among solid tumors in which chemotherapy is applied, and chemotherapy plays an important role in the overall treatment. Since surgery removes as much of the tumor load as possible, the residual tumor cells are easily killed by chemical anticancer drugs. It is generally believed that adjuvant chemotherapy should be applied early after surgery, and the effect of combined chemotherapy is better than single drug chemotherapy. Adjuvant chemotherapy should reach a certain dose and the treatment period should not be too long, about 6 months is appropriate to achieve the purpose of killing subclinical metastases. Invasive breast cancer with axillary lymph node metastasis is an indication for the application of adjuvant chemotherapy. There are different opinions on whether to apply adjuvant chemotherapy to those with negative axillary lymph nodes. Some people believe that adjuvant chemotherapy should be used except for in situ cancer and microscopic cancer (<1 cm). It is generally believed that postoperative adjuvant chemotherapy is appropriate for those with negative axillary lymph nodes but with high-risk recurrence factors, such as primary tumor diameter >2 cm, poor histological classification, estrogen and progesterone receptor negativity, and overexpression of oncogene HER2. The CMF regimen is commonly used and can be started as early as possible after surgery (within 1 week) depending on the condition. The dose is cyclophosphamide 400mg/m’, methotrexate 20mg/m2 and fluorouracil 400mg/m2, all administered intravenously, once on day 1 and once on day 8, for 1 course of treatment, repeated every 4 weeks, and 6 courses of treatment are completed. Because the effect of applying Adriamycin alone is better than other anticancer drugs, CAF regimen (cyclophosphophthalamide, Adriamycin, fluorouracil) can be applied to cases with poorly differentiated and late stage tumors. Cyclophosphophthalamide 400mg/m2, intravenous injection, day 1, 8; Adriamycin 40mg/m2, intravenous injection, day 1; Fluorouracil 400mg/m2, intravenous injection day 1, 8, repeated every 28 days for a total of 8 courses. Patients should have no obvious bone marrow suppression, white blood cell >4×109/L, hemoglobin >80g/L, platelet >50×109/L before chemotherapy. liver and kidney function should be checked regularly during chemotherapy, and white blood cell count should be checked before each chemotherapy, if white blood cell <3×109/L, the interval of drug administration should be extended. Those who apply Adriamycin should pay attention to cardiotoxicity. Preoperative chemotherapy is currently used mostly for stage III cases to detect the sensitivity of the tumor to the drug and to shrink the tumor and reduce the adhesion with the surrounding tissues. Drugs can be used in CMF or CAF regimens, usually with 1-2 courses of treatment. The cardiotoxic and myelosuppressive effects of epi-amycin are lower than those of adriamycin, thus making its use more widespread. Other more effective ones include vincristine, paclitaxel, doxorubicin, etc.