The reasons why babies cry at a fixed time every night include environmental discomfort, hunger and illness. 1. Environmental discomfort: baby sleep time is relatively fixed, sleep environment is too cold or too hot, sleep discomfort, crying. 2. Hunger: the baby did not eat enough before bedtime, too much activity during the day, consume too much, the middle of the night hunger, crying, should add food in time, in the usual dinner feeding should pay attention to increase dinner. 3. Disease factors: If the baby during the day to eat too much, more than the gastrointestinal tract digestive function, gastrointestinal symptoms such as bloating, abdominal pain, etc., prone to cry in the night to fix some point in time, parents should take the baby to the doctor in time. There are many reasons for babies to cry, parents should observe in time to reduce the stimulus. If the crying does not stop, you should look for the cause, timely consultation, early and clear diagnosis and treatment.