High temperature vulcanized (HTV) silicone rubber composite insulators are widely used in UHV transmission lines, and more and more attention has been paid to their ultraviolet aging resistance. In this paper, the samples of high temperature vulcanized silicone rubber come from two manufacturers, and the testing instrument is a self-designed adjustable ultraviolet aging test chamber, with 320~750 nm ultraviolet radiation as experiment condition. Then aging test by ultraviolet radiation (0, 500, 1 000 h) was carried out. Fourier transform attenuated total reflection infrared spectroscopy (ATR-FTIR) was used to analyze the relationship between the change of spectral peak and the functional group of sample (surface) before and after radiation, which was supplemented by SEM, hydrophobicity and volume resistivity measurement. Thus the aging mechanism of HTV silicone rubber was studied. The results showed that with the increase of ultraviolet radiation time, the reflection peak intensity of HTV silicone rubber side chain Si—CH3 and Si— (CH3)2 decreases, and the main chain Si—O—Si reflection peak intensity increases, the hydrophobicity decreases clearly, and the volume resistivity decreases slightly. Scanning electron microscope (SEM) showed that large particles and potholes appear on the surface of the irradiated, and the weight percentage of Al, O, Si increases. The results showed that ultraviolet light cut off the part of Si—C bond of HTV silicone rubber and removed the nonpolar methyl group from the main chain of Si—O—Si, which weakened the shielding effect on the strong polarity of the main chain. The exposed free radical —Si· was further oxidized and crosslinked, which enhanced the binding of Si—O—Si, enhanced the polarity of molecular chains, and decreased the hydrophobicity. The decrease of hydrophobicity made HTV silicone rubber easy to absorb water in the air, and the weak ionization of water itself increased the carrier concentration, resulting in a slight decrease in volume resistivity. According to the infrared spectrum analysis, the following conclusions were drawn: ultraviolet ray accelerated the aging of high temperature vulcanized silicone rubber by cutting off the functional groups on the surface of high temperature vulcanized silicone rubber; The application of infrared spectroscopy is of great significance to the study of aging of silicone rubber composite insulators at high temperature and its application in UHV transmission lines.