Chapter 11 introduces a surface grafting method of polypropylene film, which could effectively suppress the charge injection from the electrode so as to improve the insulation performance of polypropylene film under different voltage conditions (Liu et al. in IEEE Trans. Dielect Elect. Insul. 28:1264–1272, 2021;Liu et al. in IEEE Trans. Dielect Elect. Insul. 28:1539–1546, 2021;). However, there are some limitations in this method. Through the structural characterization of the modified film, it can be found that the depth of interface modification is limited, and the total amount of interface traps introduced is small, which leads to the unsatisfactory effect of inhibiting charge injection. The marginal benefit of increasing the thickness of the modified layer by prolonging the UV irradiation treatment time is gradually reduced. The further improvement of surface grafting rate and grafting depth is facing challenges.