Purpose: This study aimed to compare the contrast effects of administration via the subclavian vein, the superior vena cava and right ventricular venous tract, and the aorta in three-dimensional computed tomography angiography (3D-CTA) using one-step injection and trapezoidal cross-injection. Method: The subjects were 56 patients who underwent aortic 3D-CTA. In the one-step injection method, a 30-second injection of contrast medium was followed by saline injected at the same rate as the 30-ml contrast medium. In the trapezoidal cross-injection method, after injecting the contrast agent for 15 seconds, a variable mixture of the contrast agent and saline was injected for 15 seconds, followed by 20 ml saline injected at the same rate as the initial contrast agent injection. CT values were measured in the subclavian vein, superior vena cava, right ventricle, and aorta. Result: A significant difference was found in the subclavian vein and right ventricle, with the trapezoidal cross-injection method showing a lower CT value than the one-step injection method (p<0.01). There were no significant differences in the CT values in the superior vena cava and the aorta. Conclusion: The trapezoidal cross-injection method for aortic 3D-CTA produced lower CT values in venous pathways than those via the one-step injection method, but no changes were observed in the aortic CT values. These results suggest that the trapezoidal cross-injection method is useful in aortic 3D-CTA.