A stent graft design support system was proposed for providing information on such as the number of stent grafts, diameter and curvature of each stent graft and position of stent fixing part using multi-slice CT images. The method consisted of two parts: measurement of the parameters on such as the skeleton of thoracic aorta, maximum diameter of each cross-section including thrombus along the skeleton and position of the aneurysm on the aorta, and designing a stent graft. In order to prevent complications, designing a stent having excellent blood vessel follow-up ability. The thoracic aortic aneurysm region can be detected by extracting the thrombus. However, extracting only the thrombus using CT value was very difficult. In the proposed method, the thrombus was extracted by using CT value and its gradient strength after separating the thrombus and soft tissue using a surface of the rib. The stent was designed based on the obtained parameters. The proposed method was successfully applied to actual 200 slice of patient multi-slice CT data.