The reasons why eight-month-old babies cry at night may be physiological factors such as hunger, or disease factors such as indigestion, vitamin D and calcium deficiency. 1. Physiological factors: If the environment is too cold or too high temperature, causing the baby to feel uncomfortable; or feeding is not enough, the baby is in a state of hunger; or urine and feces, diapers need to be changed and other reasons, resulting in the baby can not sleep quietly, there will be a cry at night performance. 2. Indigestion: eight-month-old babies are young, the digestive system is not perfect, if not fed properly, causing indigestion, abdominal distension, abdominal pain symptoms, which will affect the baby’s sleep, the performance of crying at night. 3. Vitamin D and calcium deficiency: infants grow and develop faster, the demand for calcium is higher, if the body lacks vitamin D, will also affect the absorption of calcium, the body of the blood calcium is low so that the nerve excitability increases, will cause night waking, crying performance. Eight-month-old babies crying at night may also have other reasons, it is recommended to go to the hospital, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.