Polymer‐based nanodielectrics are widely used in microelectronics, aerospace and electrical insulation fields because of their excellent insulation and mechanical properties, but the strategies and mechanisms to improve their insulation strength need to be further studied. Herein, introducing MOFs (UiO‐66) particles into polyimide (PI) matrix obtained the unexpected discovery that MOFs with 3D porous structure did not degrade the insulation strength and mechanical stretching of composite films, conversely, remarkably increased the breakdown strength (Eb) and mechanical strength at low doping concentration. With only 1 wt% doped of UiO‐66, the maximum Eb of UiO‐66/PI composite film is 458.6 kV/mm, which is about 64% higher than PI (279.8 kV/mm). To study the mechanism of performance improvement, the interface structure was characterized by synchrotron radiation small‐angle X‐ray scattering, and the interface influence factor is introduced to modify the classical dielectric model. It was found that the hydroxyl groups on UiO‐66 can form hydrogen bonds with the PI molecular chain, and this strong interaction at the interface is the main reason for the performance improvement of low‐content doped composites. This study provides a strategy for improving the insulation properties of composites at low doping and offers some insights into the application of MOFs in high performance dielectrics.