Excellent overall performance, including high breakdown strength, brilliant flexibility, and fine mechanical properties, are hard to achieve simultaneously in polymer‐based composites. It is a challenge to improve the electrical properties of the polyimide (PI)‐based composites and to restrain the degradation of mechanical properties even at high doping content. Herein, PI/boron nitride nanosheets (BNNs)‐titanate nanotubes (TNs) ternary composite films are designed via interfacial construction of BNNs‐induced partial orientation TNs with uniform dispersion process, achieving high breakdown strength (175.3 kV mm–1), excellent tensile strength (163 MPa), large elongation at break (67%), and outstanding storage modulus (3023 MPa). Micro‐sized one‐dimensional TNs and nano‐sized two‐dimensional BNNs form a spatial network structure through hydrogen bonding, which can significantly inhibit the degradation of the mechanical and electrical properties of the composites. The orientation of TNs induced by BNNs and interface behavior between nanofillers and PI matrix are investigated and theoretical analysis using the finite element simulation is carried out to demonstrate the influence of BNNs on the electrical performance of the composites. This work can shed light for designing of high insulation and superior mechanical strength functional materials.