Gastrointestinal bleeding is a common and serious clinical condition. The GI tract includes the oropharynx, esophagus, stomach, duodenum, jejunum, ileum, cecum, colon, rectum and anus. Endoscopy is very meaningful for the diagnosis of acute upper gastrointestinal bleeding and is now commonly accepted, but often the cause remains unclear in some patients with endoscopy, especially in patients with lower gastrointestinal bleeding. For patients with GI bleeding of unknown cause and location, it is recommended to perform multi-phase (plain, arterial, portal and delayed) enhanced scans of the abdominopelvic MSCT, which can localize the bleeding according to the manifestations such as contrast spillage, and is especially suitable for arterial bleeding, with an accuracy rate of 100% for bleeding localization. In addition, radionuclide imaging can be used to detect the site of active bleeding.