The invention discloses a lightweight sound-absorption heat-insulation polyimide foamed material, and a preparation method thereof. The preparation method comprises following steps: an aromatic dianhydride, a low molecular alcohol, a surfactant, and an auxiliary agent are mixed at a certain ratio, and are reacted in a polar solvent so as to obtain a foam precursor solution; the foam precursor solution is reacted with isocyanate in a mould, and semi-free foaming is carried out so as to obtain a foam intermediate; microwave radiation treatment, and heating curing in an aging oven are carried outso as to obtain the lightweight sound-absorption heat-insulation polyimide foamed material. The preparation route is short; the preparation method is simple; the foam precursor solution is low in viscosity and high in stability, is suitable for casting and extrusion process; the foaming process is simple, and is convenient to control; defects such as cracking, collapsing, nonuniformity, and incomplete material imidization are avoided; the obtained lightweight sound-absorption heat-insulation polyimide foamed material is high in stability and strength, is low in density, possesses excellent sound absorption and heat insulation performance, and can be widely used in fields such as aerospace, ship, automobile, refrigeration house, and other special application fields.