All the cancer patients receiving radiotherapy should routinely undergo three-stage diagnosis of malnutrition after cancer diagnosis or admission to the hospital. The three-stage diagnosis of malnutrition includes nutritional screening, nutritional assessment and comprehensive measurement. NRS-2002 is recommended for nutritional risk screening, and PG-SGA is recommended for nutritional assessment. Conventional nutritional therapy is not recommended for cancer patients. We should correctly assess the nutritional status of patients using PG-SGA and acute radiation injury during radiotherapy according to RTOG criteria. According to the results of the comprehensive evaluation, patients who are malnutrition or at risk of malnutrition will receive nutrition therapy in time on the basis of the treatment path. The five-step nutrition treatment principle is also adopted for the radiotherapy cancer patients, and the four-step principle is adopted for the choosing of enteral nutrition pathway. Prophylactic implantation of nutrient tube before radiotherapy is not recommended unless the patients has one or more of the following situations: significant weight loss (greater than 5% within one month or greater than 10% within six months), BMI less than 18.5, severe dysphagia or painful swallowing, severe anorexia, dehydration, and prospective severe radiation-induced oral or esophageal mucositis. The recommended amount of energy intake for radiotherapy patients with malignant tumor is 25~30kcal/(kg·d). It should be adjusted dynamically according to tumor burden, stress state and acute radiation injury during radiotherapy. We should reduce the proportion of carbohydrates and increase the proportion of protein and fat supply in the total energy supply. Glutamine is beneficial in reducing the incidence of radioactive skin toxicity and severity of radiation mucositis. Omega-3 PUFA is beneficial for improving immune function and regulating inflammatory response in patients undergoing radiotherapy. It is recommended that glutamine and Omega -3 PUFA be added to the enteral nutrition formula. Doctors should evaluate the efficacy and adverse reactions of enteral nutrition according to the reaction speed of different observation indexes during radiotherapy. Radiotherapy patients with malignancies who are out of hospital should be given home enteral nutritional support and management if they are still suffering from inadequate intake of nutrients through mouth, or who have the nutrient tube dependence.