Left abdominal pain and blood after colonoscopy may be caused by intestinal mucosal injury. Colonoscopy is an invasive examination, usually the colonoscope is put into the anal canal through the anus, and a small amount of gas will be injected into the intestines in order to observe the situation in the intestines, in the process of operation, the colonoscope may produce friction on the intestinal mucosa, which may lead to mucous membrane ulceration and bleeding, resulting in the symptom of pain and bleeding in the left abdomen. Colonoscopy is usually used for diagnosis of gastrointestinal bleeding, colorectal cancer, colorectal polyps, enteritis and other diseases, and it is recommended that the patient under the guidance of the physician, strictly follow the requirements of the medical staff to cooperate, so as to avoid injuries during the examination. Patients can go to the hospital in time for treatment if they find that the bleeding is relatively large and symptoms such as high fever and chills occur.