Objective To compare the sensitivity of MDCT combined with different tube voltages in diagnosis of gastrointestinal bleeding. Methods The average CT value of the 30 patients with alimentary tract bleeding (all confirmed by pathology) was (212.13 ± 64.54) HU, which served as the reference value. A concentration of 6.4 mgI/ ml was prepared with Iodine fo alcohol (320 mgI/ml) and 0.9% normal saline; 120 kV corresponds to CT value of (214.73 ± 1.63) HU. Under the same contrast concentration (6.4 mgI/ml), the injection rate of 0.3 ml/min, 0.4 ml/min, and 0.5 ml/min was performed with microinjection pump. MDCT scan was carried out on the gastrointestinal bleeding model. Control group: 120 kV, 300 mAs; Experimental group A: 100 kV, 300 mAs; Experimental group B: 100 kV, 400 mAs; Experimental group C: 80 kV, 465 mAs Radiation dose, objective noise value and SNR, recognition rate of hemorrhage, CT value of the bleeding point were recorded by two double-blind radiologists. Results CT volume dose index (CTDIvol) and effective dose (ED) were significant different among 4 groups (P < 0.05). There was no statistically significant difference between the group B and control group in image noise, SNR, image quality subjective score (P > 0.05). Detection rate of the model hemorrhage was 100% in all 4 groups when the bleeding rate was 0.5 and 0.4 ml/min. Control group, group A and group B failed to detect bleeding when bleeding rate was 0.3 ml/min. The detection rate of hemorrhage of 0.3 ml/min was (2/7) in group C, which was increased significantly when compared with control group (P < 0.05). Conclusions Under normal scanning conditions, MDCT is able to identify bleeding point (0.4 ml/min); reduction of the tube voltage effectively increases the CT value of the bleeding point.