Lactose intolerance is a non-infectious diarrhea, or even chronic, prolonged diarrhea, caused by low lactase secretion and inability to completely digest and break down lactose in breast milk or cow’s milk, which can cause nutritional deficiency and growth retardation in infants and children in severe cases, also known as lactase deficiency. Diarrhea and other symptoms often occur in newborns and infants whose main diet is breast milk. The causes of lactose intolerance in infants and young children are different, the clinical manifestations are diverse, the duration varies, and the severity varies, specifically as follows. 1, gastrointestinal manifestations: the main symptom is diarrhea several times a day to more than 10 times a day, most of the children have more intestinal gas, often bringing out a small amount of feces on the diaper. The stool is mostly yellow or greenish thin paste, or egg-flake soup-like, sour smell, foamy, with milk lumps, and a few children have milk reflux or vomiting. The child may also have gastrointestinal symptoms such as bloating, diarrhea, nausea and belching. They tend to cry before defecation and improve after defecation or treatment. 2, systemic symptoms: such as headache, depression, inattention, memory loss, etc. 3, long-term will affect the absorption of calcium: cause pediatric rickets, chondromalacia and osteoporosis, etc.. Severe lactose intolerance can lead to serious consequences such as anemia, malnutrition, and growth retardation. For those with severe lactose intolerance, a lactose-free or low-lactose diet should be adopted according to the degree of the disease. And pay attention to the supplementation of calcium and phosphorus.