The baby’s sudden crying at night may be caused by various factors such as fright, fever, calcium deficiency and so on. 1. Scare, if the baby usually let the daytime play more excited or frightened, may have an impact on the baby’s night sleep, the symptoms of sudden night crying. 2. Fever, if the baby has a fever, the body temperature rises, accompanied by headache, sweating, resulting in the baby’s physical discomfort, so this symptom will appear. 3. Calcium deficiency, if the baby’s body calcium deficiency, may have an impact on neuromodulation, so there will be the symptom of crying at night. The baby suddenly cries at night, there may be 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.