Objective To investigate the effect of different injection rate of contrast medium on the quality of multislice spiral CT portography(SCTP). Methods Thirty patients with no prominent difference in the age and weight randomly divided into 3 groups (10 cases each group) underwent contrast-enhanced CT scan of abdomen. Non-ionic contrast medium (300 mgⅠ/ml, 1.5 ml/kg) was injected through antebrachium veins with power injector at the rates of 2.0 ml/s,3.0 ml/s and 4.0ml/s. Arterial phase acquisi-tion was made using the software of automated bolus triggering with a ROI placed on abdominal aorta when 100 HU was reached, and 7 seconds and 20 seconds later, portal phases were done respectively. The attenuations of portal vein(PV) and hepatic parenchy-ma of 3 groups were measured on source images. Then the oblique axial and coronal maximum intensity projection(MIP) maps were reconstructed at workstation and PVs were observed. Statistics analysis was made with software of SPSS 11.5. Results The attenu-ations of PV in 2.0ml/s, 3.0 ml/s and 4.0 ml/s groups were (150.80±21.16)HU, (170.90±17.26)HU and [181.90±22.88) HU respectively. There was obvious difference between 2.0ml/s and 4.0ml/s groups for atteuation of PV(P=0.017). The differences of CT attenuation of PV-hepatic parenchyma in three groups were (50.20±17.40) HU, (67.10±23.08) HU and (76.20±22.75) HU respectively. Prominent difference was also found between 2.0 ml/s and 4.0 ml/s groups(P=0.039). The grades of segment of PV displayed on SCTP maps were 4.20±1.14,4.90±0.99 and 5.50±0.53 in 2.0 ml/s,3.0 ml/s and 4.0 ml/s groups respectively, which were of obvious differences between them (P=0.013). Conclusion Injection rate of contrast medium dose influence the quality of SCTP of PV,SCTP quality is best with velocity of flow at 4.0 ml/s.