In this thesis, the software system in CAD and the designing method for the 2$\frac{1}{2}$-D contour design are presented and B-spline curve which is used underlying mathmatical basis in this system are stated. Any designer (the user of this system) designs any contours which can be used in various CAD and CAM fieldes by using this system. Since this system provides the designer with many interactive facilities, any user can simply design the objects interactively. For controllability and compactability of the shape the generalized B-spline curves are used in this system. This system is implemented on CYBER-170 and TEKTRONIX 4015-1 graphic terminals in KIST for the purpose of practical use in various CAD fields.