In both power systems and aerospace electrical fields, with the increasing application voltage levels of equipment, the use of traditional polyimide (PI) films as insulation materials is prone to corona discharge and even insulation failure, it is difficult to ensure the safe operation of equipment. In order to improve the thermal conductivity and corona resistance of polyimide films, this experiment adopts a synergistic modification of polyimide with carbon nanotubes (CNT) with good conductivity and high mechanical strength, and 10% doped silicon carbide. We investigate and evaluate the properties of modified composite films with different components, and explore the optimal formula for synergistically improving the comprehensive performance of composite films. The experimental results show that (10% SiC + 0.7% CNT)/PI composite films have the best comprehensive properties, and the 5% mass loss temperature is 30 ℃ higher than that of pure PI film, the thermal conductivity and tensile strength of PI film were increased by 95.7% and 22.53%, respectively, and the first long-flow discharge and flashover time were 332 min and 372 min, respectively, which were 672.09% and 500% higher than those of PI film, respectively, the threshold field strength of the nonlinear conductivity is 4.30 MV/m, which is favorable for promoting space charge transport in high field strength.