Abstract: Energy storage film capacitors, which possess an ultrahigh power density, high operating voltage, high self-healing and high reliability, are widely applied in smart grids, electric vehicles, and power conditioning. However, the low energy storage density and large dielectric loss of polymer dielectric materials limit the development of lightweight, miniaturization and reliability of energy storage film capacitors. In this paper, the latest research progress based on optimization of composite dielectric materials with high energy storage density and low dielectric loss is reviewed, involving the structural properties, dielectric properties, electrical strength and energy storage mechanism of composite dielectric materials. Several factors for improving the energy storage characteristics of polymer dielectric materials are compared and analyzed. A variety of strategies are also analyzed, including multi-component inorganic filler co-filling, nano surface modification, multi-layer structure composite, molecular structure design, surface deposition coating and other methods for improving the energy storage characteristics and regulation mechanism. Finally, the existing challenges and future directions of high energy storage polymer dielectric materials are summarized and prospected.