During radiotherapy, tumor patients often do not eat enough to meet their daily nutritional needs, resulting in weight loss, and often need to supplement nutrition with oral nutritional preparations on the basis of optimal diet, so how to supplement is scientific? There are two points that need to be noted as follows: (1) high energy density (drink a small amount of nutrients to provide as much energy and protein as possible); (2) appropriate high fat and low sugar formula (adapt to the metabolic characteristics of tumor patients, tumor cells like sugar); (3) high protein formula (protein is the most needed by tumor patients) taste should be good (patients can supplement for a long time); (4) Low osmotic pressure (not easy to have diarrhea). 2. Precautions for supplementation When drinking in the early stage, it must be slow and start with small amount, like tasting tea, otherwise the intestine will not adapt to the high concentration of nutritional preparation, which will lead to diarrhea. To heat it properly, just warm it up with hot water over a cup. If diarrhea still occurs, consider reducing the dose or changing the formula, as each patient’s intestinal adaptation is different and should be managed individually. The dose will be gradually increased after adaptation, usually reaching the target required amount in 3-5 days. The model often used is 3+3 model, that is, in addition to breakfast, lunch and dinner, one supplementation of nutritional preparation at 9:00 a.m., 3:00 p.m. and 8:00 p.m. The amount of supplementation is decided according to the actual amount of meals, about 100-200ml each time, which is very helpful to reach the daily nutritional amount and to maintain the weight and physical status. Oral nutritional supplementation is the most common and practical nutritional treatment for tumor patients.