The conventional methods for finger-vein structure description could not fully describe the distinct and steady line-structures of finger-vein. Therefore, a finger-vein structure description method based on B-spline was proposed. The new method obtained the coordinate set of all target points on every finger-vein branch by using line scanning operation on thinned finger-vein images. A B-spline function was used to fit the curves of finger-vein branches. The control-point coordinates of every B-spline curve were gained, and they were used to describe the line-structures of finger-vein. Experiments show that the new method can availably describe line-structures of finger-vein with little description error and small storage space requirements. Furthermore, this method can improve the recognition rates of finger-vein.