Babies are always crying, may be caused by physiological factors such as hunger, may also be due to intestinal flatulence, vitamin D deficiency and other pathological factors caused by severe crying or accompanied by other symptoms, should be promptly consulted to identify the cause. 1. Physiological reasons: hunger is a relatively common reason for babies to cry, may also be urine and stool, and need to be pacified and other factors caused by the phenomenon is normal. 2. Pathologic causes: (1) intestinal flatulence: refers to a variety of reasons, such as incorrect breastfeeding posture or feeding when crying, etc., resulting in the baby’s intestinal tract to accumulate a large amount of gas and can not be discharged in a timely manner, which can lead to abdominal pain, abdominal distension and other symptoms of the affected child and cause crying. (2) Vitamin D deficiency: Children with vitamin D deficiency may have symptoms of irritability and sleep disturbance, which may lead to crying, especially at night, and in severe cases, may lead to bone changes and delayed motor development. Parents should pay attention when their babies cry for a long period of time, or when they are accompanied by other uncomfortable symptoms. They should bring their babies to the hospital in time to find out the causes and have them treated accordingly by the doctor if necessary.