Five months baby always sleep on his back may be related to the lack of security, abdominal discomfort, cold and so on. 1. lack of security: baby sleeping on his back may be emotional fluctuations during the day to be frightened, etc., sleeping on his back will feel a sense of security. 2. abdominal discomfort: baby indigestion, abdominal distension, abdominal pain, etc., this time sleeping on the stomach abdominal muscle tension will be relieved, thus alleviating abdominal distension, abdominal pain symptoms. 3. Colds: the baby may have a cold with nasal congestion symptoms, sleep on the stomach can relieve nasal congestion, relieve discomfort, in the cold when the baby is easy to sleep on the stomach. Five months baby always sleep on his back, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor’s treatment.