Nanocomposite polymer materials are commonly used in energy storage devices on account of the excellent dielectric performance. However, there is a long-standing contradiction between dielectric constant and breakdown strength of nanocomposite. In this study, polyurea (PUA) is designed to in situ modify BaTiO3(BT) nanoparticles. Based on the excellent dispersity, favorable compatibility and outstanding insulating performance of BT@PUA particles, the P(VDF-CTFE)/BT@PUA nanocomposite exhibits enhanced breakdown strength and reliability. In addition, the introduction of BT@PUA enhanced the dielectric constant to 10.72 and 35% larger than that of pure P(VDF-CTFE). As a result, the energy density of BT@PUA composite reaches 8.94 J/cm(3), which is 1.65 times than P(VDF-CTFE) (5.41 J/cm(3)) and 4.5 times than the commercial biaxially oriented polypropylenes. Meanwhile, the quantified simulation illustrates the necessity of extremely high breakdown strength of the shell. Experiment results and simulation reveal that coating PUA is a novel and effective way to enhance energy storage performance for polymer nanocomposites with a promising broad application prospect.