Abstract: The segmentation of pulmonary vessel is a challenging problem because of its tiny vessel, noisy CT image and blurred boundary. A method based on threshold level-set is therefore proposed for the 3-D segmentation of pulmonary vessel, which introduces the geometric contour-varying models instead of parametric contour-varying ones. As a result, this method is available to solve the inaccuracy of blurred boundary of the pulmonary vessel by determining the range of threshold of the position of pulmonary vessel and its distribution in accordance to anatomical structure. Thus, the segmentation of pulmonary vessel can be done more accurately. In addition, a judging scheme of branching node of pulmonary vessel tree is proposed on level-set basis.