Due to the superior thermal and dielectric properties of polypropylene（PP）

PP becomes a suitable candidate for thermoplastic insulator of high-voltage direct-current（HVDC） cable. In this paper

both nano-SiO

2

and polyethylene octene（POE） were introduced in PP matrix

in order to modify the crystalline and improve the electrical and mechanical properties. The morphology

DC breakdown strength

space charge distribution

crystallization behavior and mechanical properties were characterized by scanning electron microscopy（SEM）

polarized light microscopy（PLM）

AC/DC breakdown system

pulsed electro-acoustic system（PEA）

differential scanning calorimeter（DSC）

and electronic universal testing. The results showed that the DC breakdown field was enhanced

the space charge was inhibite

d and the mechanical properties were improved in the composite with the co-doping of nanoparticles filling and POE blending. The breakdown strength increased by about 25% and the elongation at break increased by about 30% in the composite compound of PP

POE and nano-SiO

2

compared with raw PP sample. The modification of mechanical and dielectric properties provides promising results for the application of PP in HVDC cables.