Abstract: Polyphenylthiourea (ArPTU) is a new type of high breakdown, low loss material. In order to improve its energy storage density, ArPTU can be blended with poly(vinylidene fluoride)(PVDF). The problem that how to improve its solubility and reduce the interface during blending with PVDF has become one of the research hotspots. Modification with dopamine (DA) can effectively improve its interface with PVDF. DA modified ArPTU-PVDF(DA/ArPTU-PVDF) composite films with different blending ratios were prepared by solution casting hot pressing method and characterized by X-ray diffractometry, scanning electron microscopy, nuclear magnetic resonance, gel permeation chromatography and impedance analyzer. The results show that when the mass fraction of DA/ArPTU is 10wt%-15wt%, the relative content of β crystal form of PVDF increases remarkably, which is one of the main reasons for the increase of dielectric properties. At 100 Hz, the dielectric constant can be the largest. It reaches 10.3 (10wt% DA/ArPTU), while the dielectric loss decreases, and the minimum reaches 0.008 (25wt% DA/ArPTU). The energy storage density of the composite material also increases significantly, up to 3.0 J/cm³ (10wt% DA/ArPTU), which is 63.3% higher than that of the pure PVDF. In addition, the breakdown characteristics of the composites are greatly improved compared to the pure PVDF, up to 556.4 MV/m (15wt% DA/ArPTU). Moreover, the mechanical properties of the modified composites have also been greatly improved. The maximum elongation at break can reach 196.7% (5wt% DA/ArPTU), showing the potential of flexible high breakdown energy storage materials.