Early recovery, when hemodynamics are not yet stable or when there is a severe metabolic acidosis phase, is not a safe time to start nutritional support. In addition, it is necessary to consider the metabolic changes in different stages of different primary diseases, and also the characteristics of organ function. The presence of severe hepatic failure, hepatic encephalopathy, severe azotemia, and severe hyperglycemia without effective control makes it difficult to implement enteral nutritional support effectively. Critically ill patients with hemodynamic stability and the presence of gastrointestinal function should be given appropriate nutritional support within the early 24 hours. Nutritional support in critically ill patients should be started as early as possible, and enteral nutrition should be actively adopted as long as the anatomy and function of the gastrointestinal tract allow and can be used safely. If the patient has contraindications to enteral nutrition or enteral nutrition is not tolerated and normal nutrition is not expected within 3 days, parenteral nutrition needs to be started within 24-48 hours.