The dog's belly suddenly swells greatly, which may be caused by indigestion, ascites, etc. If the dog appears to be in poor spirits, vomiting and diarrhea, or has an elevated body temperature, it is best to take the dog to the pet hospital for examination and treatment; if If there is no abnormality, then it is caused by improper diet and indigestion. You can feed the dog some probiotics to regulate the stomach.