The invention belongs to the technical field of nano porous aerogel material preparation and particularly relates to a preparation method of a polyimide aerogel film which has flexibility, low density, high strength and low thermal conductivity. By adopting a sol-gel method, a polyamide acid solution is synthesized by dianhydride and diamine as monomers, (aminophenyl) polyhedral silsesquioxane is taken as a crosslinking agent, and a gel film can be continuously prepared through a chemical imidization process; the high-performance polyimide aerogel film is further prepared by adopting a supercritical drying technology. The reaction process is simple, the prepared film is good in flexibility, can be bent, and contains abundant nano mesopores; and the density is 100mg/cm<3>, the tensile strength reaches 11.4MPa, and meanwhile, the polyimide aerogel film has good heat performance, heat insulation effect and insulating effect, and can be used for a flexible coated thermal insulation and insulating material, so that ultrathin, fine and multi-level development of the flexible coated material is achieved.