The early life(including the fetus, infants, and young children) is a critical period for the establishment of intestinal flora. More studies have shown that the establishment and evolution of intestinal flora in early life will affect children’s health even in adulthood and is closely related to the future nervous system, immune system, endocrine system and other diseases. The establishment of its intestinal flora is affected by various internal and external factors such as prenatal maternal factor, mode of delivery, feeding methods, gestational age, use of antibiotics, probiotics, and environmental factors.