A one-year-old baby suddenly crying at night may be due to physiological factors such as fright during the day or pathological factors such as respiratory tract infections. 1. Physiological factors: the baby in the daytime by the shock, or sleep due to light, large sound and other external factors interference, thus the phenomenon of sudden crying, parents appropriate appeasement of the child, may ease the crying. 2. Pathologic factors: may be due to calcium or vitamin D deficiency, respiratory tract infections and other diseases. (1) Since one-year-old children are in the teething stage, they need more calcium. If the child lacks calcium or vitamin D in the teething stage, it will cause nerve excitation and make him/her prone to sudden crying at night. (2) Due to respiratory tract infections, thus nasal congestion, difficulty in breathing and other symptoms, leading to the phenomenon of children crying. A one-year-old baby suddenly crying at night, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.