The relation has been set up for the figure of the grid and the convexity of surface in terms of geometry concept by analysing the relationship between the necessary and sufficient conditions of local convex on Bezier surface and the figure of control vertices grid,a couple of necessary and sufficient conditions for local convex on Bezier surface are then educed.The conclusion of convexity analysis is applied to Bezier surfaces splicing,the condition of convexity-preserving splicing for Bezier surfaces is derived.Moreover,it is proved that afte...