Compound amino acid dipeptide injection is part of parenteral nutrition solution, which mainly replenishes amino acid in human body and further facilitates protein synthesis, especially for patients with partial water fasting or patients who need parenteral nutrition for a long time, they can be supplemented with compound amino acid dipeptide injection in appropriate amount. For patients with parenteral nutrition, appropriate supplementation of fat milk and protein is also needed. As patients who fasted water, their body is mostly in negative nitrogen balance, with moderate as well as severe catabolic and metabolic state, patients should pay attention to the amount of compound amino acid dipeptide injection supplementation, and see whether patients have any contraindications to parenteral nutrition. For patients with underlying phenylketonuria and systemic cardiovascular failure or other complications, we should actively consider whether the patient is suitable for parenteral nutrition. For patients with parenteral nutrition, attention should be paid to the regulation of intestinal flora, because the long-term application of parenteral nutrition will lead to the dysbiosis of intestinal flora, after the formation of pathogenic bacteria, causing intestinal infections, the appropriate amount of nasal feeding tube or gastric tube injection of intestinal probiotics to regulate the intestinal flora.