The study design is a randomized controlled study. The eligible criteria is all patients who undergoing major gastrointestinal surgery including upper/lower gastrointestinal tract and hepatobiliary and pancratic surgery. After the informed consent are obtained. The patients are randomized into two group (study group and conventional group). The perioperative supplement with oral nutritional support and dietary advice were assigned in the study group. The conventional group were assigned only dietary advice. The blood test and nutritional assessment are performed by investigators in all participants. The participants were assessed two times before the operation (at first assigned and the day before the operation). The duration of nutritional supplement is at least fourteen days.The patient characteristic data, surgical intervention, and postoperative data were collected. The main outcome is the postoperative morbidity and mortality.