Abstract: Cancer malnutrition observed in 31%~87% patients with cancer can reduce the tolerance and compliance to radiotherapy,interrupt or delay the treatment,and significantly affect the prognosis.The malnutrition may be aggravated when the duration of radiotherapy is prolonged and chemotherapy is applied concurrently.PG-SGA is the most suitable method for nutritional risk screening in patients with malignant tumor.According to the result of nutrition assessment,giving the adaptive nutrition support can improve the nutritional status of patients and the curative effect in the early stage of radiotherapy,as wells as post radiotherapy.