Polypropylene　has　great　potential　as　a　thermoplastic　insulation　material　for　high　voltage　direct　current　(HVDC)　cable.　However,　its　mechanical　properties　restrict　its　application,　particularly　at　low　temperature.　In　this　paper,　isotactic　polypropylene　(iPP)　with　the　β-nucleating　agent　WBG　was　prepared　by　the　melt　blending　method.　The　crystallinity,　β-crystal　proportion　and　crystalline　morphology　were　analyzed　by　wide-angle　X-ray　diffraction,　differential　scanning　calorimetry,　scanning　electron　microscopy　and　polarized　optical　microscopy.　The　results　showed　that　the　crystallinity　and　β-crystal　proportion　increased　as　the　WBG　concentration　increased.　Three　types　of　β-crystal　morphology,　namely　β-spherulite,　flower-like　agglomerate　and　β-quasi-spherulite,　were　sequentially　obtained　with　increasing　WBG　concentration.　The　mechanical　properties,　space　charge　distribution,　thermally　stimulated　discharge　current　and　DC　electrical　breakdown　strength　were　investigated.　Compared　with　pure　iPP,　the　Izod　impact　strength　and　DC　breakdown　strength　of　iPP/0.1%WBG　were　improved　by　238　and　16%,　respectively,　and　the　fracture　energy　and　brittleness　temperature　of　iPP/0.3%WBG　were　improved　by　420　and　80%,　respectively.　In　addition,　the　space　charge　accumulation　was　suppressed　in　the　range　of　0.1-0.5　wt%　WBG.　Chain　coupling　between　the　β-crystals　and　the　amorphous　phase,　particularly　in　the　flower-like　agglomerates,　was　considered　to　play　an　important　role　in　improving　the　mechanical　and　electrical　performance.　©　2019　IEEE.