Integrated multidisciplinary treatment is the basic principle of breast cancer treatment, which includes the participation of diagnostic radiologists, pathologists, surgeons, medical oncologists and radiation oncologists to determine the most rational treatment strategy for the patient. Radiotherapy and surgery complement each other and are an extremely important tool in the local treatment of breast cancer. The use of radiation therapy for breast cancer has been around for more than a century, but it really matured technically after the development of Co60, high-energy X-rays and brachytherapy in the 1950s. On the one hand, improvements in radiation therapy equipment and advances in radiation biology and radiation physics have continued to lead to technical refinement; on the other hand, as the understanding of the biological behavior of breast cancer has progressed, so has the radiation oncologist’s understanding of the place of radiation therapy in the comprehensive treatment of breast cancer. From the holistic view of comprehensive treatment, the main purposes of radiation therapy in breast cancer treatment include the following: i. Radical radiotherapy after breast-conserving surgery for early-stage breast cancer is an integral part of breast-conserving treatment. Radiotherapy not only reduces the local recurrence rate by 2/3, but also the irradiation technique directly affects the cosmetic effect of the breast and the quality of patient survival. Second, postoperative radiotherapy of the chest wall and regional lymph nodes after selective mastectomy in stage I and II patients can effectively reduce the local recurrence rate and improve the survival rate to some extent. Third, one of the necessary means of comprehensive treatment for patients with locally advanced disease. Fourth, radiation therapy for patients with local regional recurrence is an important remedial treatment measure. V. Palliative radiotherapy for metastatic patients, such as pain relief for patients with bone metastases, prevention of pathological fractures and spinal cord compression; reduction of intracranial hypertension for patients with brain metastases and relief of neurolocalization symptoms caused by metastases; hemostasis of ulcerative recurrent foci in the chest wall, etc., improves the quality of survival of patients in the period of survival with tumor and prolongs the survival time of some patients.