Pain on the left side of the stomach mainly refers to the left side of the mid-abdominal pain, this place is the most common of the following conditions: 1, there may be gastrointestinal diseases, such as acute and chronic gastroenteritis, intestinal spasms, gastrointestinal tract dysfunction, or localized intestinal polyps or tumors, which can cause pain in the left abdominal area. 2, it may be a disease of the urinary system, for example, urinary stone or urinary infection, if the urinary stone, the pain appears suddenly and the pain is very severe, accompanied by pallor, nausea, vomiting, percussion pain in the left kidney area. Infection, if it is urinary stones, the pain is suddenly appeared, and the pain is very intense, accompanied by pale, nausea, vomiting, left kidney area percussion pain and other symptoms. If it is a urinary tract infection, there will be frequent urination, urinary urgency, urinary pain, and even fever.3. There may be some gynecological diseases, such as acute or chronic pelvic inflammatory disease, endometriosis, or dysmenorrhea, which can cause pain in this place.