Abstract: In recent years, accidents in flexible cable terminals for high-speed locomotives have occurred frequently under extreme ambient operating temperatures, which has seriously impaired the safety of railway transportation. According to the extreme temperature (–40~90 ℃) of actual locomotive operation, the influence of extreme temperature on the interface pressure of cable and accessory insulation is discussed by comparing and analyzing the elastic modulus change of silicone rubber materials used in cable accessories in the process of high temperature, low temperature, and high-low temperature cycle and the stress relaxation characteristics under the expansion state. The results show that the interface pressure relaxation rate of the expanded silicone rubber material is nearly 30% at a high temperature of 90 ℃, is 10%~20% at a low temperature of –40 ℃, and is as high as 50% after 120 h of high-low temperature cycles (–40~90 ℃). Therefore, a significant decrease in the interface pressure of cable and accessory insulation under extreme temperatures may have a significant impact on the insulation performance of locomotive cable terminals.