Thermoplastic polypropylene material has excellent electrical and thermal properties. It does not require cross-linking and degassing in the production process of power cable insulation, has low energy consumption and good environmental friendliness, and can be recycled compared with cross-linked polyethylene. In this paper, medium-voltage polypropylene cable and cross-linked polyethylene cable insulation were used as the research object. The directly synthesized polypropylene and cross-linked polyethylene were analyzed by differential scanning calorimetry, Fourier infrared spectroscopy, and X-ray diffraction analysis, and their mechanical tensile properties, dielectric constant and loss, breakdown strength, and other macroscopic properties were tested. The results show that the structure of the directly synthesized polypropylene is interspersed with ethylene segments, which leads to the melting temperature of polypropylene material decrease, but its melting temperature is still much higher than that of the cross-linked polyethylene. The ethylene segment will participate in the crystallization process of polypropylene, but will not crystallize alone. The elongation at break of polypropylene is 712%, which is higher than that of the cross-linked polyethylene (566%), which is more conducive to the transportation and installation of cable. The breakdown strength of polypropylene at 90℃ is 91.5 kV/mm, which is 123% higher than that of the cross-linked polyethylene at the same temperature, and the breakdown strength of polypropylene has better stability with respect to temperature. In terms of comprehensive mechanical properties and electrical properties, the performance of directly synthesized polypropylene is not inferior to cross-linked polyethylene, which can be used as an insulating material for medium voltage cables.