Abstract: The energy contained in intense ultraviolet (UV) radiation in high-altitude regions is sufficient to alter the molecular structure of silicone rubber, leading to severe aging phenomena in composite insulators, thereby, increasing susceptibility to insulation failure. However, existing studies rarely address the physicochemical characteristics of composite insulators in strong UV environments. Moreover, the stochastic variability of meteorological parameters in natural environments differs from the fixed parameters in laboratory settings, leading to significant discrepancies between UV radiation aging patterns observed in controlled experiments and those occurring under natural conditions. Therefore, the insulators deployed in the power grid for varying durations from two distinct regions, namely, Qinghai Province (a typical high-altitude area with strong UV radiation) and Shandong Province (a region with relatively weak UV radiation), were selected as research subjects in the current research. Through comparative analysis, the impact of UV aging on the physicochemical properties and electrical performance of the insulators were investigated. Additionally, molecular dynamics simulations were employed to explore the cleavage mechanism of Si-O-Si bond. The results indicate that in high-UV regions, the contents of Si-(CH3)2, C-H in (CH3) and Si-CH3 groups all exhibit decreasing trends with increasing operational duration. However, the Si-O-Si content shows a biphasic pattern, that is, initially increasing and then decreasing with operational duration, due to the varying dominance of oxidative crosslinking and cleavage processes at different stages. In contrast to Qinghai Province, all group contents in Shandong Province decrease with operational duration. Concurrently, with increasing operational duration, the O/Si atomic ratio of composite insulators in Qinghai Province rises from 1.19 to 1.37, while the contents of Si(-O)3 and Si(-O)4 groups increase from 23.48% and 11.50% to 58.84% and 21.75%, respectively. Under the same operational duration, the insulators in Qinghai Province exhibit higher O/Si ratios and greater Si(-O)3 and Si(-O)4 contents than those in Shandong Province. These findings indicate that intense UV radiation accelerates methyl group loss and surface inorganic transformation processes. Consequently, the static contact angle of the insulators in Qinghai Province decreased by 22.1%, compared to only 6.3% in Shandong Province. With increasing operational duration, silicone rubber crosslinking structures of composite insulators in both regions are damaged, accompanied by surface morphological deterioration. This damage introduces physical and chemical traps on the surface, leading to a decrease in flashover voltage. In Shandong Province, the crosslinking structures of the insulator shed exhibit more severe damage, resulting in a higher density of physical traps. The increased accumulation of the charges on the insulator surface caused a greater disruption to electric field uniformity compared to the insulators in Qinghai Province. Consequently, under the same operational duration, the insulators in Shandong Province demonstrate lower flashover voltages than those in Qinghai Province. Molecular dynamics simulation results reveal that the high temperatures generated by insulator discharges exacerbate silicone rubber pyrolysis. Under the combined effects of electric field and temperature, alterations in Si-O-Si bond energy occur. When the bond energy drops below 427 kJ·mol-1, UV radiation induces the cleavage of Si-O-Si bond. The research findings present in this paper provide theoretical support for the aging assessment and operational maintenance of composite insulators in strong UV regions.