Selective laser sintering (SLS), a powder-based 3D printing process, has been increasingly employed for end-use applications in aerospace, automotive, medical and many other sectors because of its great design freedom, high precision, and reproducibility. A numerical model has been developed to predict the temperature distributions and dimensions of melt pools in SLS and optimize the processing parameters. The model has been applied to guide the printing of newly developed carbon nanotubes-reinforced polymer nanocomposites, and the printed parts have demonstrated superior thermal, electrical and mechanical performances. Furthermore, lightweight structures including auxetic lattices have been designed and printed to show their energy absorption and dissipation applications.