A month baby dilute water stool has physiological factors, may also be lactose intolerance, rotavirus infection and other pathological factors. 1. Physiological factors: the digestive system of one-month-old babies is not well developed, if the weather suddenly becomes cold, the abdomen is cooled, causing an increase in intestinal peristalsis leading to dilute watery stools, or due to the sudden change in the weather, the baby ingested too much milk caused by dilute watery stools. It is recommended to keep the abdomen warm and keep the room temperature constant. 2. Pathologic factors: (1) lactose intolerance: a month old baby who lacks lactase enzyme or the activity of lactase enzyme is reduced can cause loose watery stools. (2) rotavirus infection: it can cause infantile rotavirus gastroenteritis leading to loose watery stools. It is recommended to take Montelukast orally under doctor’s guidance. One-month-old babies may also have other causes of watery stools, it is recommended to go to the hospital in a timely manner, improve the examination to determine the cause of the disease, under the guidance of the doctor to give targeted treatment or therapy.