Polypropylene has become a hotspot in the research and development of thermoplastic cable insulation materials due to its advantages of high working temperature, excellent insulation performances and recyclability. The molded joint employs the same insulation material as the cable body as joint insulation, which can not only find a solution for the movable interface of the prefabricated joint, but also help to realize the recyclability of the whole PP cable line system. Firstly, a 10 kV PP cable molded joint is manufactured, and the crystal structure, electrical performances and mechanical properties performances of the PP cable insulation and molded joint insulation slices are studied. The results show that the PP molded joint insulation sample has higher crystallinity, larger microcrystal size, and higher melting temperature compared with the cable insulation slices. For electrical performances, the molded joint insulation has higher volume resistivity, smaller tangent of dielectric loss angle, and higher power frequency breakdown field strength. For mechanical performances, the elongation at break of the molded joint insulation is smaller and the elastic modulus is larger. These differences may be due to the different processing methods of the cable and the molded joint. The cable is cooled by water cooling, and small spherulites are formed in the rapid cooling process, while the molded joint is cooled naturally at room temperature, and the PP molecular chains are fully folded and arranged to form large crystals. The different crystalline structures of PP cable and molded joint insulation lead to the differences in electrical and mechanical performances. However, the performances of cable insulation layer and molded joint insulation layer are still consistent. The results verify the feasibility of applying the molded joint in PP cables, and provide references for the further research and development of high-voltage PP cable and molded joint.