The electrical properties of polymers are closely related to their microstructure, which includes molecular structure and aggregation structure. The molecular structure of polypropylene is mainly related to the arrangement of methyl groups on the main chain of the molecular chain. In the molecular chain of polypropylene, the methyl groups connected to the tertiary carbon atoms have different arrangement modes. According to the different positions of the methyl groups, polypropylene can be divided into isotactic polypropylene (iPP), syndiotactic polypropylene (sPP) and atactic polypropylene (aPP). The methyl group of the iPP molecular chain is distributed on one side of the main chain, the methyl group of the sPP molecular chain and the hydrogen atom are regularly spaced on both sides of the main chain, and the methyl group of the aPP molecular chain is irregularly distributed on both sides of the main chain. In iPP, methyl groups are distributed on the same side of the main chain, which is easier to crystallize than aPP and sPP, and has high melting point, excellent processing performance, better electrical and mechanical properties. In addition to the molecular structure of polypropylene affecting its electrical properties, the aggregation structure of the molecular chain can also affect its electrical properties. As a typical semi-crystalline polymer, there are crystal zone, amorphous zone, crystal zone and amorphous zone interface in polypropylene. In the crystal region, the molecular chains are neat and closely arranged; in the amorphous region, the interface between the crystalline region and the amorphous region, the molecular chains are arranged disorderly and loosely. The disorder and loose arrangement of the molecular chain will destroy the periodic potential field generated by the periodic arrangement of the crystal region, affect the distribution of energy levels, and then affect the transport of carriers. Different crystal structures lead to different amorphous regions, crystal regions and amorphous region interfaces. Studies have shown that the amorphous region and the interface between the crystalline region and the amorphous region have an important influence on the breakdown strength and conduction loss of the polymer. The ash content is also a parameter that characterizes the microscopic properties of the material. Ash content is a parameter used to characterize the impurity content in polypropylene matrix. Studies have shown that some chemical structures in impurities will form a 'trap center' in polypropylene, causing space charge accumulation and causing local breakdown of the material. At the same time, agglomerated impurities cause distortion of the internal electric field of the material, resulting in a decrease in breakdown field strength. The analysis and study of the influence of these microstructures on the dielectric properties of polypropylene and the mechanism will help us to improve the understanding of polypropylene and optimize the properties of polypropylene films (Xu et al. in Polymer. 213, 2021).