Abstract: The geometric model from CAD system contains a great deal of trimmed parametric surfaces，and the adjacency relation between trimmed surfaces is very complex．At first，each surface is tessellated by subdividing all its bounding edges and joining the subdivision nodes with a regular array of isoparametric grids．Then the mesh model of all surfaces are merged together by inserting additional triangular elements to make the model compatible along all adjacent boundaries．The algorithm is fit to complex geometric model such as automobile covering part．