Energy storage media is the kernel for the rapidly developing new energy systems, while it remains a challenge to achieve admirable service capability at high temperature. This manuscript purposes crosslinking as an effective method to address the issue. The epoxy is innovatively studied as energy storage media in this research. We figure out that crosslinking density is a critical factor to determine its energy storage performance. With adequate crosslinking, attractive energy storage density/efficiency (6.9 J/cm(3)/90%@room temperature; 1.2 J/cm(3)/90% and 1.7 J/cm(3)/75%@100 degrees C) can be achieved. However, excessive crosslinking density and lack of crosslinking point are found to induce obvious energy storage performance decaying at high electric field and high temperature, respectively. This manuscript demonstrates that the general epoxy materials can be used as energy storage media and concludes that proper crosslinking can improve the energy storage performance of polymers, which provides directions for future research on high-temperature energy storage films.