Acute gastrointestinal bleeding (AGIB) is a common and serious condition that requires prompt diagnosis and effective treatment. Multi-phase contrast-enhanced computed tomography (CT) can rapidly identify the location and cause of active gastrointestinal bleeding, providing crucial information for subsequent treatment decisions, and has become a potential first-line tool for evaluating AGIB. In this report, we describe four cases of AGIB with clinical presentations of hematemesis and melena, accompanied by symptoms such as post-exertional palpitations, weakness, hypotension, confusion, and coma. Some patients also had abdominal distension, pain, dizziness, and chest tightness. The laboratory results showed anemia and positive fecal occult blood tests. Multi-phase contrast-enhanced CT allowed for the accurate localization of the active bleeding sites in the digestive tract. Among the four patients, two showed significant symptom improvement after treatment, one was transferred to a higher-level hospital due to critical illness and died from multiple organ failure, and one patient died from hemorrhagic shock due to lymphoma and multiple organ failure. This article discusses the value of multi-phase contrast-enhanced CT for the clinical diagnosis of AGIB and provides a literature review to summarize the imaging characteristics of AGIB on multi-phase contrast-enhanced CT to provide reliable evidence for the timely diagnosis of AGIB.