Abstract: Nanocomposites are widely used in microelectronics, high-voltage insulation and other fields due to their excellent dielectric, thermal and mechanical properties. Two dimensional nanofillers have drawn numerous attention because of their high aspect ratio, low surface energy and easy dispersion in the matrix and so on. Titania nanosheets (TNSs)/polyimide (PI) composite films were prepared by in-situ dispersive polymerization.The results show that the TNSs with hydroxyl are uniformly dispersed in matrix. Nanocomposites with low permittivity and high breakdown strength can be obtained by adjusting TNSs contents. The dielectric and insulating performance of composites is determined by inorganic-organic interface states. The hydroxyl group on the TNSs surface and the oxygen atom in the PI molecular chain form hydrogen bonds to construct the interface bonded region. The restricted orientation, electronic and ionic polarizabilities in the bonded region of interfaces are responsible for the reduced permittivity. The restricted polarizabilities along with the enhanced interfacial polarization determine the variation of permittivity of nanocomposites. Besides, the deep traps formed in the interface bonded region can capture carriers, which leads to the enhancement of the breakdown strength. This work provided a method to design and fabricate composite films with low permittivity and high breakdown strength.