In this paper, two methods of changing the control parameter a and changing control points are presented for the shape modification of C-Béier curves. The relation between C-Béier curves and the control parameter a is obtained based on the analysis of the derivative C-Béier basis functions. Furthermore, the way of modifying the shape by the adjustment of a is introduced. On the other hand, the algorithm of shape control by modifying control points is given relying on the model between the shape of the curve and control points. The results have been applied to the CAD/CAM system for speaker cone models, which has got a good effect.