L-carnitine is an essential nutrient that plays an important role in the process of human lipid metabolism. Premature infants are prone to lack of L-carnitine due to the characteristics of low body storage, low food intake, and strong energy metabolism. Parenteral nutrition supplementation with L-carnitine can increase the level of L-carnitine in preterm infants and improve the acylcarnitine profile of preterm infants, promote fatty acid metabolism in the early postnatal period of preterm infants, and accelerate their recovery of birth weight. Preventive use of L-carnitine before delivery by mothers can reduce the incidence of respiratory distress syndrome in premature infants. Parenteral nutrition supplementation with L-carnitine in the early postnatal period can reduce the application of pulmonary surfactant and shorten the time of mechanical ventilation in preterm infants with respiratory distress. However, the effects of parenteral nutrition supplementation with L-carnitine on fatty acid metabolism and physical growth rate in the later stages of preterm infants need to be further studied.