Abstract: To study the effects of different roughness interfaces and degassing treatment on factory joint materials and insulation characteristics of 500kV high voltage direct current (HVDC) cross-linked polyethylene (XLPE) cables, the commercial 500 kV XLPE cable pellets were injected into the surface of the sample polished by sandpaper (#80, #400, #1000, #2000, and unpolished #0000). The XLPE samples were obtained after vulcanization. The #1000 samples were degassed at 70℃ for 0, 12, 36 and 90h, respectively. Physico-chemical and electrical experiments were performed on the obtained samples. The results show that as the number of sandpaper grit meshes increases, the average lamellae thickness at the interface decreases and the crystallinity increases. Meanwhile, the elongation at break and the current density show a trend of first increasing and then decreasing, while the space charge accumulation, threshold strength and DC breakdown first decrease and then increase. Among them, the #1000 sample is the inflection point. The degassing treatment reduces the average lamella thickness and elongation at break of #1000 samples, increases the crystallinity, reduces the space charge accumulation and current density inside the sample, and increases the DC breakdown field strength. Increasing the smoothness and degassing durations of the factory joint interface can help to improve the connection between the main body and the return insulation and improve the insulation characteristics of the factory joint. But it is still lower than the main body insulation under the same conditions.