A 1-year-old baby’s sudden crying at night may be caused by physiological needs, physical discomfort, and being frightened. 1. Physiological needs: If a 1-year-old baby does not eat enough before going to bed, or has the need to defecate and urinate, sudden crying at night may occur. 2. Physical discomfort: If the baby eats too much before bedtime, the food accumulates in the gastrointestinal tract and is not digested, the baby will feel abdominal discomfort during sleep and will express this by crying. 3. frightened: it may be that the baby was frightened when playing during the day and showed it at night when sleeping, or had a nightmare while sleeping, the baby is more fearful, which led to the 1-year-old baby suddenly crying. 1 year old baby suddenly crying at night, may also be caused by other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or standardized treatment.