Gastric cancer is the most common malignant tumor in China, the ratio of men to women is 2~3:1, with the most cases occurring in 40~50 years old. The average annual mortality rate of gastric cancer in China is 25.53/100,000, ranking first in malignant tumor death. According to relevant studies, the death rate of stomach cancer in China has been on the rise since the 1970s. However, due to the atypical symptoms of early gastric cancer, most patients are already in the progressive stage when they are clearly diagnosed. Due to the limitations of early radiotherapy technology, difficulty in outlining the tumor target area, difficulty in better protection of surrounding sensitive organs (liver, kidney, spinal cord, small intestine, etc.), lack of supportive therapies, emergence of serious toxic side effects and the problem of radiosensitivity raised by some scholars, etc., gastric cancer was once considered unsuitable for radiotherapy, and radiotherapy was rarely adopted for gastric cancer. In recent years, with the conversion of treatment concept, advancement of supportive therapy, updating of chemotherapy drugs, deepening of basic research, especially with the rapid development of computer technology and imaging technology, breakthrough progress of radiotherapy has occurred. The application of radiotherapy techniques and methods such as stereotactic conformal radiotherapy, 3D intensity modulated radiotherapy, CT simulation positioning and treatment planning, outlining the target area with the help of MRT, PET-CT and evaluating the efficacy of radiotherapy, as well as the application of new radiosensitizers and radioprotective agents, have greatly improved the accuracy of radiotherapy and reduced the damage to normal tissues, which has created the conditions for radiotherapy to re-enter the field of postoperative adjuvant treatment for gastric cancer as an important local treatment. This has created conditions for radiotherapy to re-enter the field of post-operative adjuvant therapy for gastric cancer as an important local treatment, and has achieved good results in clinical application. At present, it is believed that stomach is a relatively radiation-sensitive tissue like other digestive tract organs, and gastric adenocarcinoma, like other epithelial malignancies, may be more sensitive to radiotherapy than chemotherapy. Radiation therapy for gastric cancer up to 4000~4500 cGy can clear subclinical lesions in its irradiation field. In conventional fractionated irradiation, most and all of the stomach, small intestine, and colon are largely free of serious complications after being irradiated with moderate doses at 4500 cGy level. And small-scale irradiation can even tolerate doses above 6000 cGy. In many years of clinical application, radiotherapy has been involved in the adjuvant treatment of gastric cancer in three main ways: preoperative, intraoperative and postoperative, and has achieved certain efficacy. Preoperative radiotherapy for gastric cancer refers to the preoperative local irradiation for certain progressive gastric cancer in order to improve resection rate, 200 cGy per time, 5 times/week for 4 weeks, total 4000 cGy; surgery is performed 10~14 days after stopping radiotherapy; preoperative radiotherapy can make the primary tumor of more than 60% patients have different degrees of regression, and the resection rate is 5.3%~20% higher than that of simple surgery group. Intraoperative radiotherapy for gastric cancer refers to a high-dose irradiation for the surgical field centered on the celiac artery before establishing gastrointestinal anastomosis after tumor resection, with 3000-3500 cGy as appropriate. It can improve the 5-year survival rate of progressive gastric cancer by about 10%; intraoperative radiotherapy is feasible for those with resected primary foci, lymph node metastasis within two groups, or primary foci invading the plasma surface and involving the pancreas without peritoneal and liver metastasis. Neither chemotherapy nor radiotherapy alone can improve the survival rate of progressive gastric cancer after surgery. Therefore, many scholars focus on postoperative combined radiotherapy and chemotherapy for progressive gastric cancer. They believe that for patients with progressive gastric cancer, postoperative radiotherapy combined with chemotherapy can rapidly kill local residual cancer cells and improve the local control rate of tumor cells; chemotherapy can inhibit or eliminate distant metastases of subclinical lesions and kill potential metastases, so as to obtain satisfactory survival rate. This model of postoperative combined radiotherapy for gastric cancer is based on the successful experience of adjuvant radiotherapy for rectal cancer. In rectal cancer, simultaneous radiotherapy after radical surgery has become the standard of care. In recent years in the United States, local radiotherapy combined with 5-FU-based chemotherapy after radical surgery for gastric cancer has significantly improved survival after surgery for progressive gastric cancer with acceptable toxic side effects, as demonstrated by the INT0116 trial and subsequent multi-group evaluation trials. Postoperative radiotherapy for gastric cancer can be applied to poorly differentiated tumors, tumors invading the plasma membrane, lymph node metastasis, tumors close to or positive to the incision margin, after palliative resection or exploratory surgery for gastric cancer and recurrence of gastric cancer after surgery. The dose of postoperative radiotherapy should be 4500~5000cGy, 180~200cGy each time, 5 times/week. Postoperative combined radiotherapy has become the standard treatment for progressive gastric cancer in the United States. In China, postoperative radiotherapy for gastric cancer is not yet widely practiced, and needs to be studied and discussed in depth. In our department, postoperative radiotherapy for gastric cancer has been effectively carried out, and further cases are being accumulated for analysis. The acute reactions of radiotherapy for gastric cancer include nausea, weakness, weight loss and so on. Before and during treatment, we should pay attention to the nutritional status of patients and give appropriate supportive treatment. Late complications of radiotherapy for gastric cancer include radiation damage to the spinal cord, liver, kidney and stomach. The occurrence can be avoided by paying attention to the protection of the above organs in the treatment plan design. It should be noted again that radiotherapy should be a tolerable and potentially beneficial treatment for gastric cancer.