Polypropylene (PP) as an environmentally friendly insulation material has been paid more attention. It is considered as a potential insulating material to replace cross-linked polyethylene (XLPE) for high voltage direct current (HVDC) applications. In this work, PP and PP/low-density polyethylene (LDPE) composites with different LDPE loading were prepared by melt blending method and the corresponding electrical properties were investigated. Results showed that the addition of LDPE significantly changed the microstructure of PP and the trap density was increased in the composites compared with pure PP. The conduction current of PP/LDPE composites was greater than that of PP. The electrical breakdown strength decreased at low LDPE contents and increased at high contents. Space charge was remarkably suppressed in the blend with 40 wt% LDPE loading. This work indicates that the improvements in the electrical properties, especially the charge transport and space charge suppression in the composites are closely related to the trap level density.