One of the reasons for vomiting is the cat needs to get some fur balls up. Another possibility is that the cat is allergic to the cat food it is eating.
The most common reason is hairballs. When cats lick themselves, sometimes they swallow their own fur and that can cause nausea. Talk to a vet about good hairball control food.
A cat is always grooming itself. During the course of day when it is grooming itself it will ingest some of this hair. This hair will come out as vomit.
