Abstract: The environmental friendly cable insulation material represented by polypropylene (PP) is a research hotspot at present. The influence of graft modification on the thermal oxidative aging properties of PP materials and its mechanism were studied. The results show that before the antioxidant content reaches the threshold, the thermal oxidative aging reaction is mainly limited in the amorphous regions and the oxidation reaction rate is low. In this process, the crystal structure tends to be perfect under the action of heat, which improves the electrical properties, while the partial degradation of the amorphous structure leads to the significant reduction of the tensile properties of the samples. After the antioxidant content reaches the threshold, the oxidation reaction rate intensifies, the structures of amorphous regions and crystalline regions degrade seriously, and the sample loses its insulation performance in a short time. Compared with pure PP, the grafted samples can form small spherulite structure and unique crosslinking structure, inhibit the diffusion of oxygen into the interior of the sample and reduce the oxidation reaction rate, so the thermal oxidative aging performance is significantly improved. As the grafted monomer content increases, the thermal oxidative aging performance of the grafted samples is monotonously improved, and the 10% Styrene (St) grafted sample has the relatively best thermal oxidative aging performance. The research results provide a theoretical reference for improving the long-term operation performance of PP cable insulation.