The left side of the stomach vague pain and blood in the stool, that is, the left side of the abdomen vague pain, blood in the stool, may be related to ulcerative colitis, colon polyps, colon cancer and other diseases, the specific situation needs to be determined according to the patient’s clinical manifestations and related examination, under the guidance of the doctor symptomatic treatment. 1, ulcerative colitis: due to bacterial, parasitic infection and autoimmune low and other factors, resulting in inflammatory changes in the colon, will make the colon wall The ulceration occurs, the left side of the abdomen vague pain, as well as will be accompanied by mucus pus blood stool, diarrhea and other symptoms. It can be treated by oral administration of salazosulfapyridine enteric tablets, sodium olsalazine capsules, ciprofloxacin hydrochloride tablets and other drugs; 2, colon polyps: may be due to genetics, bacterial infection and other factors, causing active proliferation of intestinal mucosa, resulting in polyps, the growth of polyps will pull the surrounding blood vessels, resulting in blood vessel rupture, the phenomenon of vague pain on the left side of the abdomen, blood in the stool. Colon cancer: It is a malignant tumor originated from the epithelial cells of colon mucosa. When the tumor grows to a certain extent, it will stimulate the colon and cause vague pain on the left side of abdomen, accompanied by blood in stool and change of bowel habit. It can be treated by surgical removal and the use of drugs such as bevacizumab injection and cetuximab injection.