Radiotherapy has been used for nearly a century now. At present, malignant tumors have become a common and frequent disease in countries all over the world. The incidence rate is increasing year by year, and the mortality rate accounts for the first or second place of various causes of death. Radiation therapy has become one of the main means in the treatment of malignant tumors, and more than 70% of tumor patients need radiation therapy (including comprehensive treatment and individual treatment). Some malignant tumors can be treated with radiation therapy alone to achieve good curative effect. Moreover, radiation therapy has become a specialized discipline, called radiation oncology, including clinical radiation physics, clinical radiobiology and clinical radiotherapy. And it has developed rapidly in the past 40 years. Some early malignant tumors have high cure rate with radiation therapy alone, such as early nasopharyngeal cancer, cervical cancer, vocal cord cancer, Hodgkin’s lymphoma, skin cancer, etc. The 5-year survival rate of early esophageal cancer, prostate cancer, tongue cancer, etc. are similar to surgery, while the functional cosmetic preservation is more satisfactory. Generally, 70% to 80% of the tumor patients who come to hospital are already middle to late stage patients. Most of them cannot be operated, or have difficulties in resection, or have contraindications to surgery, or are unwilling to operate, most of them need to perform radiotherapy, and many of them have better results. Radiation therapy also plays an important role in the comprehensive treatment of tumors, such as preoperative, intraoperative and postoperative radiotherapy with surgery; radiotherapy before, during and after chemotherapy with chemotherapy; and comprehensive treatment with radiation therapy, surgery and chemotherapy. In conclusion, radiation therapy is an indispensable and important treatment for most patients with malignant tumors. Patients with malignant tumors should pay attention to consultation and treatment in radiation therapy department.