Radiotherapy is one of the most important and cost⁃effectiveness treatment for malignant tumors. Although it can improve the nutritional intake and status of patients, its adverse reactions may lead to the occurrence of malnutrition or the deterioration of nutritional status. Malnutrition will have adverse effects on patients with malignant tumor undergoing radiotherapy. Standardized and effective nutritional treatment is of great significance, which is conducive to maintaining the weight of patients, reducing the adverse reactions of radiotherapy, and improving the completion rate and therapeutic effect of radiotherapy. The purpose of nutritional therapy for radiotherapy patients includes: ① to diagnose and treat malnutrition before, during and after radiotherapy; ② to reduce the adverse reactions of radiotherapy, to enhance the radiotherapy tolerance, reduce the unplanned interruption of radiotherapy, and improve the radiotherapy completion rate; ③ to increase the sensitivity of tumor cells to radiotherapy, improve the accuracy of radiotherapy, and improve the short⁃term and long⁃term efficacy of patients; ④ to improve the quality of life of patients.