Compared with the traditional insulation materials such as cross-linked polyethylene（XLPE）

polypropylene（PP） is famous for its better recyclable and thermal properties

as well as good electrical performance. Therefore

selecting PP such as propylene-ethylene copolymer and homo-polypropylene as base resin materials

we studied the influence of adding nano magnesium oxide（MgO） on PP’s insulation. First

we prepared a series of nano-composites with 0.5%

1%

2%

and 3% MgO contents

and tested the direct current（DC） breakdown strength of samples. According to the main insulation parameters such as DC breakdown strength

the optimum additive content of MgO is 1%. Second

1% nano-MgO and 5% ethylene-octene elastomer（POE） were added to PP matrix through two different processes to compare the nanocomposites in the presence of pure PP and the blend of PP/POE. Finally

the microstructure

mechanical property and electrical property of all samples were characterized. Results show that nano-MgO

as heterogeneous nucleating agent

can reduce the size of sphaerocrystal and induce the generation of β-crystal in PP. Adding nano-MgO to PP hardly affects the mechanical property. However

it reduces space charge of PP greatly. There was no significant differences in DC breakdown strength and DC superimposed impulse voltage between PP and XLPE. Recyclable thermoplastic PP is a new option for HVDC cable in the future.