Malnutrition is very common in patients with COPD. The main reasons include short intake of energy and systematic inflammation. In our randomized and controlled clinical trial, patients will be divided into two groups: the experimental group and the control group. Patients in the experimental group will be provided nutritional supplements in addition to usual diet every day for three months and patients in the controlled group with usual diet. According to the changes of patients' body composition, anthropometrics, inflammatory markers, lung function, respiratory muscle function, exercise capacity, degree of dyspnea and health related quality of life(HRQL) after intervention，the nutritional status and inflammation status are assessed, which contributes to the prediction of prognosis. The nutritional supplements is a kind of oral liquid composed of proteins, omega-3 fatty acids, carbohydrate, vitamins, which provides about 260 kcal energy per 200ml. The patients from the interventional group need drink the nutritional supplements according to the estimated energy intake and a record should be made everyday. The patients will be followed up regularly by the researcher.