Abstract: PMI foam is known with excellent mechanical properties and high strength to weight ratio, lightweight, high strength sandwich structure of the core material, in particular for the production layered Materials, laminated materials, composite materials, etc. In this article, Polymethacrylimide ( PMI) foams were prepared by the casting process using methacrylic acid (MAA) and acrylonitrile (MAN) as monomers. The structure and properties of the PMI foams were analyzed by infrared adsorption spectrum (ATIR), optical microscope, differential scanning calorimeter (DSC) and thermo gravimeter (TG). The results show that the foamable MAA/AN copolymers were prepared at 47-70 °c by polymerizing the mixture of 50phr MAA, 50phr AN, 2-5phr 2-propanol and 0.1-0.3phr azo-bis izobutironitryl. Then the resulting copolymers were expanded at 200-220 °c for 1-2 h, subsequently treated at 160 °c for 5-6h. The main purpose is investigating the effect of processing parameters on the chemical properties of PMI with high heat resistance. The processing parameters which should be investigated are the temperature, the method of mixing and foaming agent. Molecular rearrangement reaction occurs during the foaming and post treatment forming hexahydric imides ring. The prepared PMI foams have closed cell structure and have a good cell size with the characteristic degradation Temperature at about 180 °c. Key words: methacrylic acid; acrylonitryle; polymethacrylimide; Foams.