The diagnostic criteria of severe malnutrition are mainly measured from five aspects: 1. weight, if the weight loss exceeds 5% in one month or 10% in 6 months, the presence of severe malnutrition should be considered. 2. nutritional intake, if the nutritional intake is reduced by more than 75% than usual, there may be severe malnutrition. 3. nutrition-related symptoms, such as nausea, vomiting, bloating, diarrhea. If such symptoms are obvious, it is necessary to consider the existence of severe malnutrition. 4, whether there is a heavy functional decline or progressive aggravation, such as walking disorder, self-eating disorder. 5, physical examination, such as subcutaneous fat, thin limbs, including finger sunken edema, from these five aspects can basically determine whether the patient has severe malnutrition.