Babies always cry in the middle of the night may be related to the environment, lack of vitamin D and digestive problems. 1. Environment: If the baby is in an environment where the room temperature is not suitable or the cover is not suitable, it is easy to cause the baby to cry in the middle of the night, parents can pay attention to the room temperature and the cover. If there are noisy sounds around the house in the middle of the night, it may also cause the baby to cry in the middle of the night. 2. Vitamin D deficiency: if the baby in addition to midnight crying, there are irritable, occipital baldness and other manifestations, it may be vitamin D deficiency. 3. Digestive problems: baby crying in the middle of the night, first consider whether the baby is hungry, not enough feeding before bedtime is easy to cause frequent crying at night. If the baby is not hungry, it may also be too much feeding before bedtime, resulting in baby indigestion, abdominal distension and abdominal pain. There are other reasons why babies always cry in the middle of the night, parents can take their children to the hospital for examination to determine the cause.