To investigate the effect of the interface electronic structure of core-shell quantum dots on the conductivity and space charge characteristics of polyethylene insulation, nanocomposite insulations, namely CdSe@ZnS/LDPE and ZnSe@ZnS/LDPE, are synthesized. The study focuses on elucidating the evolution patterns of DC conductivity and space charge in the nanocomposite insulation, and analyzing the effect of the interfacial electronic structure of core-shell quantum dots on the distribution of charge traps. Comparative analysis reveals that in contrast to LDPE insulation, ZnSe@ZnS/LDPE nanocomposite insulation demonstrates a substantial reduction in DC conductivity by 47.2% and a decrease in space charge accumulation by 40.3% under the conditions of elevated temperature and strong electric field. The increase of trap energy level means an enhanced trap effect on charger carriers. According to density functional theory, the band structure characteristics of core-shell quantum dots integrated with polyethylene are computationally assessed. The findings underscore that the band misalignment at the core-shell interface and the shell-insulation interface induces shifts in the conduction band bottom and at the valence band top, respectively. These shifts impose a confinement effect on electrons and holes, with the extent of this effect escalating with the augment of the difference in band gap between the core layer and the shell layer. Consequently, this phenomenon curtails carrier migration, thereby inhibiting space charge accumulation under the conditions of elevated temperature and strong electric fields.