Abstract: The establishment of topological mesh problem in point clouds preprocessing was researched. To solve the problem obtaining the correct topological relations of the scattered point clouds, a sort of triangulation based on incremental growth was researched for point clouds. Searched the nearest neighbors of boundary points by using the algorithm of k-nearest neighbors quickly, it constructs triangles based on the boundary ring of incremental algorithm, and realizes the construction of topological mesh. Three new criteria were presented for the selection of the optimal points, and three operations of mesh topology based on the different position of the optimal points was given out to construct new triangular mesh,which the triangulation could be proceeded precisely. The overlapping , pore as well as long and narrow triangles were eliminated. The application for the point clouds of auto body indicates that triangulation mesh of body surface can be constructed effectively and steadily.