A series of polyurethane / melamine-formaldehyde resin interpenetrating network rigid foam was synthesized by stepwise IPN method. It was characterized by apparent density, compressive strength, bending strength, flame resistance and cell structure. The results showed that with the increase of polyurethane content, the apparent density of foam plastics decreased, and the mechanical properties of foamed plastics were improved effectively. However, after adding 20%  polyurethane, the mechanical properties were not obviously increased , and the foams changed from high inflammable materials, inflammable materials to flammable materials.