This paper presents an intuitive sketching tool for human-computer interactively designing and modeling the vascular structure. Our system supports freehand outlining of the initial vascular structure through a 3D user interface, which is capable of modeling tubular vessel segments as well as bifurcations. The editing capability can be used for completing partially segmented vascular information such as the topology and radius, as well as designing normal vascular structure or pathological vascular structure such as the aneurysm and stenosis for medical simulations curriculum. Our tool may also be used in the various semi-automatic initialization steps for segmentation and registration processes such as the positioning of 3D seed and land-marking of vessels on top of different modalities. The improved parallel frame approach is used for sweeping surfaces along the composed curve of vascular tree such that the vascular structure can be easily and well visualized as a tube model.