A novel rigid polyurethane thermosetting foam is synthesized via the reaction of isocyanate terminated polyimide prepolymers with polyether polyol(4110), and deionized water and n-pentane are used for blowing agents simultaneously. The prepolymers and polymers are characterized by conventional methods and -NCO conversion rate, characteristic structure and morphology are also studied. The results show that the optimal condition of polymerization of polyimide prepolymers is under 60 oC for 30min. FTIR data show that the imide groups have been achieved successfully. The rigid polyurethane-imide foams prepared by this technique possess the cell diameter ranging from 1.5mm to 2.5mm and bubbles distributing equably.