Polypropylene insulated cables taking advantages of good thermal resistance and recyclability are highly attractive for applications in power networks, which have become the direction of recyclability cables development in the future. The gradient effect of polypropylene insulated cables in the radial direction has an important impact on the overall performance of the cables. In this paper, the cable insulation samples were prepared by the ring cutting method, and the insulation properties and radial gradient effects of the grafting modified polypropylene cable at 30℃ were investigated. The test results show that there is no significant difference in DC volume conductivity and space charge density at different positions in the radial direction of the cable insulation, and the electrical properties of the cable insulation are relatively uniformly distributed in the radial direction. It shows a better ability to suppress space charge injection, and there is very little space charge injection inside the sample at room temperature. The crystalline form, melting temperature and crystallinity of grafting modified polypropylene at different radial positions also basically coincide, considering that the temperature gradient effect in the cable manufacturing process is not obvious, the overall aggregate state structure of the cable insulation has not changed significantly, and the electrical properties in the radial direction are stable without gradient effect. This study lays a good foundation for the development and application of polypropylene cables.