Infants crying at night may be related to environmental factors, improper feeding, lack of vitamin D, gastrointestinal diseases and other factors. 1. Environmental factors: the infant’s thermoregulatory center is not well developed, if the indoor temperature is too high or wear too much clothing, it may lead to an increase in body temperature, so that the baby feels uncomfortable, and cry at night. 2. Improper feeding: If the amount of breast milk secretion is too little to eat, it will be easy to appear hungry at night, resulting in night crying. In addition, if the amount of formula is too much to eat too full, it may be bloated and uncomfortable, causing the phenomenon of night crying. 3. Lack of vitamin D: In the process of physical development of infants, the lack of vitamin D in the body, may lead to rickets, the emergence of night crying, accompanied by night terrors, excessive sweating, occipital baldness and other undesirable phenomena. 4. Gastrointestinal diseases: when the baby suffers from intestinal spasm, intussusception and other diseases, it may lead to abdominal pain, the emergence of night crying, accompanied by vomiting, diarrhea, pallor and other symptoms. After excluding environmental factors and improper feeding, parents should bring their babies to the hospital for relevant examinations, and actively treat them after clarifying the causes.