The causes of vague pain in the left upper abdomen are mainly the following: Firstly, it is considered to be caused by the disorder of digestive and absorption functions of the intestinal tract of the body, mostly due to the usual diet inattention, overeating or eating more spicy and stimulating food, etc., resulting in the peristaltic digestive and absorption functions of the intestinal tract being affected, thus causing vague pain in the upper abdomen. The second cause is due to acute and chronic gastritis and gastric ulcer, etc. The left upper abdomen is distributed with stomach, if the usual diet is not careful or acid reflux, etc., which stimulates the gastric mucosa and causes ulcers, it will cause vague pain in the left upper abdomen. The typical manifestation of gastric ulcer pain is that the pain is aggravated after meals, and the pain caused by duodenal ulcer is mostly aggravated in fasting, so you need to go to the hospital for barium meal or gastroscopy of the upper gastrointestinal tract to clarify. The third reason is the slow intestinal peristaltic function, which causes intestinal obstruction, resulting in vague pain in the left upper abdomen, due to the slow intestinal peristaltic movement, which leads to the obstruction of intestinal contents out of the body, causing pain.