Abstract: An interactive approach is proposed for B-spline surface editing to improve the distribution of curvature lines on surface. In order to indicate a more regular distribution of curvature lines and to decrease the number of umbilical points, desired curvature lines are plotted on surface interactively. The plotted lines are used as target curvature lines in an optimization algorithm for surface modification, which becomes approximate curvature lines on surface after optimization. The effectiveness of the proposed method is demonstrated by several B-spline surface models.