Abstract: In order to study the effect of nano conductive particles with different microscopic morphologies on the direct current (DC) dielectric properties of low-density polyethylene (LDPE), polypyrrole (PPy) nanospheres and nanowires with a diameter of about 100 nm were prepared by soft template method, and melt blended with LDPE to obtain PPy/LDPE nanocomposites. The microscopic morphology of PPy nanoparticles and their dispersion structure in PPy/LDPE nanocomposites were observed by scanning electron microscopy (SEM). The crystallinity, space charge distribution, dielectric spectrum, and DC conductive current and DC breakdown strength of the composites at different temperatures were tested. The results show that the addition of PPy nanoparticles can improve the crystallinity of LDPE, inhibit the accumulation of space charges in LDPE and reduce the relative dielectric constant, DC conductive current and DC breakdown strength. The addition of PPy nanospheres can reduce the DC conductive current of LDPE by more than one order of magnitude at different temperatures, but has little effect on its DC breakdown strength, and can increase the DC breakdown strength of LDPE by 4.4% at a higher temperature. The improvement effect of PPy nanospheres on DC dielectric properties of LDPE insulation materials is better than that of PPy nanowires.