In electromagnetic railgun technology, the performance of pulse power supplies significantly affects the efficiency and stability of launching systems. Recently, film dielectric energy storage materials have gained attention for their high energy density, rapid charge-discharge capabilities, and excellent thermal stability, making them central to pulse power research. This paper reviews advancements in these materials, focusing on the performance and application potential of polymer-based composites and nanostructures. Polymer-based composites are favored for their lightweight and processability; incorporating conductive fillers can enhance their dielectric properties. Nanostructured materials also show promise, as nanoparticle dispersion improves electrical characteristics. This paper discusses practical applications of various dielectric materials in railgun systems and the challenges encountered. Looking ahead, advancements in materials science will likely expand the application prospects of dielectric energy storage in pulse power, driving further developments in electromagnetic railgun technology.