Abstract: In strong ultraviolet (UV) radiation, silicone rubber materials (high temperature vulcanized (HTV) silicone rubber and liquid silicone rubber (LSR)) for outdoor insulation are deteriorated, threatening the operation safety of transmission lines. To study the influence of UV-A radiation on both silicone rubber materials, the experiments about microstructure (X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer) and operation properties (thermal stability, mechanical and electrical properties and crosslinking density) of LSR and HTV silicone rubber were conducted. It was found that after 1000h UV-A aging time, for HTV silicone rubber, the carbon element decreased about 13.4% while oxygen element increased about 10.0%. And methyl, thermal stability and mechanical strength decreased. In contrast, for LSR, the carbon element increased about 5.8% while oxygen element decreased about 7.6%. Si(—O)₄ structure decreased while methyl content increased about 65.7% and thermal stability were improved. It is also found that the difference of UV-A resistance between LSR and HTV silicone rubber is caused by crosslinking structure, ATH content and hydrogen containing silicone oil. Based on proposed hydrogen abstraction reaction during UV-A radiation process, the UV-A resistance of LSR can be enhanced by reducing the amount of hydrogen containing silicone oil and by increasing the molecular weight of raw rubber. This paper can provide support for understanding the UV aging characteristics of silicone rubber materials for outdoor insulation, and guide the selection of outdoor insulation materials in high altitude areas.