Breastfeeding babies spit up as soon as they drink formula milk, considered to be caused by improper feeding, unaccustomed, milk allergy, gastrointestinal diseases and other factors. 1. Improper feeding: Generally speaking, breastfed babies are fed on demand, without special measuring tools. And when breastfeeding babies eat milk powder, if they accidentally soak too much milk powder and feed too much at once, it can lead to the baby can not be digested in time, thus causing spitting up. 2. Unaccustomed to: eat used to breastfeeding babies, it is generally difficult to accept formula feeding, so for some breastfeeding babies, direct feeding of formula, may not like the phenomenon of spitting up because of unaccustomed, belonging to the expression of emotions of an action. 3. Milk allergy: some babies are allergic to certain substances contained in milk powder, so it is easy to trigger an allergic reaction to milk powder, leading to vomiting, diarrhea and other symptoms. 4. Gastrointestinal diseases: babies have gastrointestinal lesions, such as acute gastroenteritis, can also lead to babies drink milk powder on the phenomenon of vomiting. So when a breastfeeding baby drinks milk powder and vomits, you need to find out the cause of the disease in time and carry out reasonable treatment.