Polymer nanocomposites have been extensively studied for dielectric energy storage applications, however, the relatively low breakdown strength due to inevitable defects and voids limits themselves in the development of the high energy density capacitors while large-scale manufacturing. Herein, we propose a facile strategy to improve the breakdown strength and thus energy density by synergistically designing the intermolecular structure in a ternary polymer blend composed of poly(methyl methacrylate), poly(vinylidene fluoride), and poly(vinylidene fluoride-hexafluoropropylene). We show that the appropriate quenching temperature can decrease crystal size and increase the fraction of the amorphous phase. Meanwhile, by designing the mass ratio of the ferroelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-hexafluoropropylene), it will successfully introduce the intermolecular interaction, which stabilizes the γ-phase in ferroelectric polymers and leads to dense chain packing. All the phenomena contribute to the ultrahigh breakdown strength (850 MV/m), and the optimized blend exhibits a record high discharged energy density of 30 J/cm3. Of particular importance is that a large-area dielectric film with high property uniformity can be fabricated, demonstrating that the proposed design approach can be used as a general technology for mass production.