The energy storage performance of film capacitors will deteriorate sharply at high temperature, which is difficult to meet the demands of aerospace and energy fields. Therefore, it is necessary to study the degradation mechanism of energy storage performance of energy storage film at high temperature. Polyurea is a linear dielectric with high energy storage density and low dielectric loss, which can be used as a high-performance dielectric material for film capacitors. To investigate the effect of thermal-oxidative aging on the dielectric energy storage performance of polyurea films, the polyurea films were treated with thermal oxygen for different days, and the dielectric and energy storage performance before and after thermal-oxidative aging were tested and analyzed. The test results show that the dielectric constant and the DC breakdown field strength have the same change trend, in the early stage of thermal-oxidative aging, it decreased slightly, and in the later stage, it increased significantly and then decreased. Therefore, the energy storage performance of the thermal-oxidative aging samples showed a trend of decreasing first, then increasing, and finally decreasing significantly. Among them, the energy storage density is as high as 6.39 J/cm3 at 16 days of thermal-oxidative aging, which is due to its high breakdown field strength of 586 MV/m.