Sudden crying in infants is generally considered to be caused by physiological manifestations, vitamin D deficiency and colic. 1. Physiological manifestations: normal babies mainly through crying to express emotions, hunger and urination and defecation may have the phenomenon of crying, timely breastfeeding or cleaning after urination and defecation, can be quickly improved. 2. Vitamin D deficiency: infants lack of vitamin D can lead to rickets, neuromuscular sensitivity increases, the performance of sweating, irritable, difficult to fall asleep, suddenly wake up crying and so on. After holding up and soothing, it can usually be temporarily relieved. 3. Intestinal colic: infants suddenly cry, pick up or breastfeeding can not be soothed, the performance of the limbs curled up, and accompanied by abdominal distension, defecation abnormalities, etc., is considered to be intestinal spasm caused by crying. Babies suddenly cry for a variety of reasons, it is recommended to combine the baby’s specific situation to identify, crying and difficult to appease the mental state with bad, to the hospital in a timely manner, clear causes under the guidance of the doctor to standardize the treatment, to avoid delays in the condition.