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Composite insulators, which use high temperature vulcanized (HTV) silicone rubber as shed material, are widely applied in transmission lines. Ice accumulation on their surfaces may inflict flashover accident and even massive power outage. In this study, a superhydrophobic (SH) coating on HTV silicone rubber was fabricated by the sol–gel process combined with the plasma jet treatment method. It was found that the as-prepared SH coating exhibited prominent superhydrophobicity and an excellent self-cleaning property with a water contact angle of 160.15°, a contact angle hysteresis of 0.60°, a sliding angle of 1.8°, and a surface free energy of 0.1421 mN/m. The anti-icing behavior of water droplets on the as-prepared SH coating surface was investigated at a low temperature of −30 °C and compared with that of the HTV silicone rubber surface. The results indicated that the freezing time on the SH coating was postponed obviously and was as long as 150 s. The SH coating surface exhibited about 5.6 times delay in freezing at −30 °C compared with the HTV silicone rubber surface. Furthermore, heterogeneous nucleation theory and heat transfer theory were introduced to explain the difference in freezing time between the as-prepared SH coating and HTV silicone rubber. It could be concluded that the SH coating had a large nucleation free energy barrier and a low heat transfer rate between the droplet and the surface and, thus, was able to effectively delay the freezing time.