To achieve the localization of HVDC cable insulating materials and guarantee the long-term operation reliability of DC cable system, test samples are parepared by two typical formulations of DC cable XLPE insulating and semiconductive shielding materials. The elementary component and molecular structure characteristics of the test samples are analysed by using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) in order to evaluate the performance of cable insulating material. Furthermore, the thermal and mechanical properties are experimentally investigated to study the changes of thermal conductivity and mechanical performance before and after thermal aging test. The comparison and analysis of the experimental results may provide basic experimental data support for future HVDC cable system engineering design and material selection, and forming a fundamental DC insulating material quality evaluation system.