The main function of lactase is to promote digestion and absorption in the gastrointestinal tract of infants. Lactase is an enzyme-like substance mainly found in breast milk, which can play an important role in promoting digestion and avoiding diarrhea and bloating in infants’ digestive system. Clinically, it can be used to prevent constipation and diarrhea, and increase the amount of nutrients in the body, as a nutritional product, which is beneficial to the body. Lactase can be broken down into various monosaccharide substances in the body. It plays an important role in the development of bone and brain in infants, and lactase promotes brain development and maintains the basic metabolism of infants. Timely supplementation of breastmilk during infancy and early childhood will supplement lactase for infants, prevent constipation and diarrhea, and promote growth and development of infants.