The physicochemical properties and dielectric properties of cross-linked polyethylene (XLPE) insulated cables can change under long-term thermal aging, affecting their electrical behavior, such as the growth process of electrical trees. This paper investigates the impact of thermal aging on the growth characteristics of electrical trees in XLPE cable insulation. Electrical tree growth tests were conducted on accelerated thermally aged samples, and differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and broadband dielectric spectroscopy tests were used to study changes in the microstructure and dielectric properties of XLPE materials. The results indicate that recrystallization reactions and thermal-oxidative reactions are the main causes of changes in crystallinity (Jc) and carbonyl index (Q), which subsequently lead to changes in polar molecules within XLPE. This results in a trend where dielectric parameters initially decrease slowly and then increase rapidly. The study also found significant correlations between the thermal aging evaluation indicators (Jc, εr, and tanδ) and the growth rates of electrical trees at 10kV (G10) and 12kV (G12). Equivalent relationships between G10, G12, and the thermal aging evaluation indicators were established through polynomial fitting analysis. Given the known physicochemical properties and dielectric properties of XLPE materials, the degree of electrical tree aging in XLPE cable materials can be determined, providing a reference for cable insulation assessment and lifespan prediction.