For patients at nutritional risk who need nutritional treatment, enteral nutrition should be preferred if there is no contraindication. Enteral nutrition is widely used in acute and critical diseases, inflammatory bowel diseases, perioperative management of gastrointestinal surgeries, and non-mild acute pancreatitis. The basic and clinical research on the mechanism of enteral nutrition therapy has become a hot topic in recent years. The majority believe that enteral nutrition therapy works through regulating mucosal immunity and intestinal microecological balance, but the underlying mechanism is still unclear. This review is focused on the mechanism of action of enteral nutrition, in order to inform future application in disease management and the selection of enteral nutrition formulations.