Stomach pain when having diarrhea is usually related to acute gastroenteritis, Crohn’s disease, irritable bowel syndrome and so on, as follows. 1. Acute gastroenteritis: it is due to the repeated stimulation of the gastrointestinal mucosa by inflammation, resulting in decreased gastrointestinal function, increasing the burden on the intestinal tract, easily causing indigestion, diarrhea, abdominal pain and other symptoms. 2. Crohn’s disease: it is a chronic non-specific inflammatory disease, usually related to infection as well as environmental and autoimmune factors. During the active phase, symptoms will recur and be prolonged. Some patients may have acute abdomen, manifested as diarrhea and abdominal pain. 3. Irritable bowel syndrome: it is a kind of non-organic functional bowel disease, which is usually affected by dietary environment, mental and other factors, and repeated stimulation is easy to cause acute diarrhea, abdominal pain and so on. The old pain in the stomach when having diarrhea may also be caused by malignant tumors, such as rectal cancer, colon cancer, and so on. It is recommended to observe first, if long-term diarrhea, abdominal pain, and accompanied by bleeding tendency, need to consult the doctor in time, and analyze the cause of the disease through professional examination.