Sudden crying in one-year-old babies is usually caused by environmental influences, colic, intestinal parasites and other conditions. 1. environmental impact: if the environment is noisy, suddenly loud noise or sleeping environment temperature is too high and so on may lead to one year old baby sleep suddenly crying situation. 2. Colic: Colic due to excessive intestinal gas, dietary factors, etc. may also lead to one-year-old babies suddenly cry in their sleep. 3. intestinal parasitic disease: one year old baby sleep suddenly crying may also be thus for pinworms, ascariasis and other intestinal parasitic disease, some children may also have vomiting and other symptoms. There may be other reasons why a one-year-old baby suddenly cries out in his sleep, and he should go to the hospital in time to see a doctor to clarify the cause.