Improving the surface insulation strength of substrate material polyimide (PI) is an effective strategy to suppress charging and discharging effects of spacecraft solar arrays. To meet the insulation requirements of next-generation spacecraft with higher voltage levels, the surface insulation of PI must be further improved. Herein, we propose an approach to control the surface roughness and pore distribution of PI using a pore-forming agent. Modulating surface roughness and pore distribution effectively suppresses secondary electron emission avalanches, greatly enhancing surface insulation strength. When the pore-forming agent addition ratio is 50%, the film features the highest flashover threshold of 55.93 kV, a 201.7% improvement over the PI films currently used in spacecraft. The maximum secondary electron yield decreased from 2.01 to 1.32. Additionally, this novel porous PI film is exceptionally lightweight and possesses excellent electrical and thermal properties. The thermal equilibrium temperature is up to 13.44% lower than that of PI films currently used in spacecraft. Even after high- and low-temperature thermal shock, its mechanical properties and flashover performance remain highly stable. The novel polyimide films hold great potential for future applications in insulation of space solar arrays.