6 months baby suddenly cry at night is usually due to physiological discomfort, vitamin D deficiency, intussusception and other factors. 1. Physiological discomfort: the baby in the environment temperature is too high or cover the quilt is too thick, will make the baby feel uncomfortable, leading to the baby suddenly cry at night, in addition, the baby night urine and feces wet diapers, will also make the baby feel uncomfortable, and cry. 2. Vitamin D deficiency: lack of vitamin D in the baby’s body can also appear at night the phenomenon of sudden crying, and can be accompanied by irritability, sleep disturbance, sweating, etc., and can be caused by shaking the head and rubbing the pillow pillow baldness, and will affect the baby’s development. 3. intussusception: baby intestinal peristalsis normal rhythm disorder, can cause intussusception, in addition, the baby back to the blind part of the mesentery has not been completely fixed, also easy to trigger the occurrence of this disease. After the onset of the baby will suddenly cry at night, pale, etc., and will be accompanied by vomiting, bloody stools and other phenomena. There may be other reasons for 6-month-old babies to cry suddenly at night, we suggest that they should go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.