Abstract: Objective: To measure the inferior vena cava diameters by direct and indirect MSCT angiography, and analysis whether there is difference between them. Method: Collecting 30 cases (M 14 cases, F 16 cases, ages 23~65 y, middle age 44y) which were underwent direct inferior vena cava venography, and collecting 30 cases (M 10 cases, F 20cases, ages 20~66 y, middle age 43y) of whole abdominal contrast enhanced CT, get the venous phase image. Original data were transferred to GE adw4.6 workstation for post-processing including MPR, MIP. The major axis, minor axis were individually measured, at the levels of its entrance to the right atrium, the portahepatis, the renal pelvis, above the junction of iliac vein. Measure the CT values where above 1cm the level left renal venous joined Inferior vena cava. Result: At the levels of its entrance to the right atrium, the portahepatis, the renal pelvis, above the junction of iliac vein, the major axis, minor axis of direct CT phlebography individually were (3.02 ±0.44, 2.06 ±0.32), (2.29 ±0.49, 1.39 ±0.52), (2.46 ±0.44, 1.73 ±0.45), (2.30 ±0.38, 1.66 ±0.46), of indirect phlebography individually were (2.88 ±0.43, 1.95 ±0.31), (2.37 ±0.59, 1.17 ±0.37), (2.28 ±0.32, 1.63 ±0.31), (2.25 ±0.21, 1.47 ±0.34), there is no obviously difference between them. The CT values of direct CTP where above 1cm the level left renal venous joined Inferior vena cava is (313.43 ±50.90) HU, much higher than the indirect CTV (95.50 ±22.17) HU. Conclusion: There was no significant difference between direct CTV and indirect CTV of the inferior vena cava diameters.