In product design process trends currently tend to use sculpture surface (freeform surface) that modeling by using (NURBS, B-spline, Bezier) technique to suit aesthetic, functional and manufacturability requirements. The B-Spline technique is one of the most important tools in computer aided geometric design (CAGD). This paper reported a new approach to design 3D freeform CAD model and then represented this model mathematically by using B-Spline technique. This mathematical represent consider one of the important aims that useful in manufacturing process through its geometric data which defines by this represent. The approach has three major steps: design 3D CAD solid contain freeform surface by using CAD software, analysis and extraction the parameters including geometric data of 3D CAD model based on IGES file format, and then construction the B-Spline surface of the model that contain multi patches by using basis function of the surface. The approach has been extensively tested with more than case study has 3 degrees of the surface then represented mathematically in four patches.