Pain in the left side of the abdomen can be caused by the following diseases: First, pain in the left lower abdomen is commonly caused by intestinal tumors, especially malignant tumors in elderly patients, occurring in the descending colon and sigmoid colon, the typical symptom is abdominal occult pain, also abnormal bowel movements, unformed stools, blood in the bowel movements, with the evolution of the disease, the pain will progressively increase, and in serious cases, intestinal obstruction will occur, the development of tumors The development of tumor will also lead to the occurrence of anemia and hypoproteinemia. Secondly, pain in the upper abdomen on the left side is commonly caused by gastric disease, gastric ulcer or gastritis, which can lead to aggravation of pain symptoms after eating, commonly caused by Helicobacter pylori infection, which should be treated systematically, pay attention to dietary hygiene in general, not to overeat, preferably away from the environment of tobacco and alcohol, and regular gastroscopy.