Nine-month-old babies always wake up crying in their sleep may be caused by physiological factors, gastrointestinal discomfort, calcium deficiency and other reasons. 1. Physiological factors: such as the environment is too noisy, the temperature is too high or too low, etc., may lead to nine months baby sleep always waking up. 2. gastrointestinal discomfort: usually nine-month-old babies are small, gastrointestinal function is not very perfect, susceptible to dietary influences and gastrointestinal symptoms, which may lead to the baby in the sleep is not comfortable, easy to wake up and cry. 3. Calcium deficiency: can be due to increased neural excitability, crying, accompanied by excessive sweating, occipital baldness, square skull and so on. Nine-month-old babies always wake up crying in bed, there may also be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.