Abstract: Polypropylene film is the most widely used energy storage medium in power capacitors, and its dielectric properties depend on the micro-structure of the particles and stretching process parameters. In this paper, polypropylene pellets with different isotacticity were taken as the research object, and polypropylene films were obtained by different stretching ratios. The surface morphology and crystallization characteristics of different polypropylene films were studied, the dielectric loss, breakdown strength, and energy storage chareacteristics of polypropylene films under different temperatures were analyzed. The influence mechanism of micro-structure parameters and stretching ratio on dielectric properties of polypropylene films was investigated. The results show that the polypropylene film sample with isotacticity of 99.6% and stretching ratio of 4×5 has the lowest conductivity and the highest breakdown strength. The improvement of the isotacticity can enhance the thermal stability of the molecular chain, improve the loose structure of the molecular chain in the amorphous region of polypropylene, and prevent the development of electrical weaknesses. In addition, a reasonable stretching ratio can enable the molecular chains of polypropylene to align and form an orderly crystalline morphology, and to increase the crystallinity. The research results can provide experimental and theoretical support for the improvement of dielectric properties of polypropylene films.