Abstract: In order to reveal the influence mechanism of ethylene copolymerization on the electrical properties of polypropylene (PP) cable insulation, we synthesized three types of impact PP copolymer (IPC) with different ethylene-propylene copolymer (EPR) content by two-stage impact copolymerization process, and investigated the variation of crystal structure, spherulite morphology, phase and trap distribution, mechanical and electrical properties.Results show that, when 15% EPR is introduced, the crystallinity and tensile modulus are reduced by about 6.8% and 37.4% compared with isotactic PP, whereas, the elongation at break obviously increases. The charge injection threshold field strength and breakdown strength are increased by 17.7% and 8.0%, respectively. When 30% EPR is introduced, the crystallinity decreases by 30.6% compared with isotactic PP. Meanwhile, the breakdown strength and elongation at break are still dropped. The effect of ethylene copolymerization on the macroscopic properties has been proved to be closely related to the special structure of EPR "epigenous" on the spherulites in IPC15. This study shows that proper ethylene copolymerization can realize the synergistic optimization of the mechanical and electrical properties of PP cable insulation, which can provide a reference for the regulation of comprehensive properties.