Fused deposition modeling 3D printing thermoplastic material as a raw material layer by layer print completed, because the fuse can only be deposited on the existing objects in the upper part of the model need to add support structure hanging parts.To solve this problem, an automatic support structure generation algorithm based on STL (Stereo Lithography).Algorithm to obtain an independent area to be supported, based on the edge-length adaptive method and ray and patch intersection method to be supported point set to automatically generate the support structure.In addition, the support structure is prevented from growing on the surface of the model and the shape of the support structure is adjusted.Experiments show that the proposed algorithm saves 15% of the material consumption compared with Cura software, the support structure is more easily peeled off and the surface quality of the model is better.