The operational environment of China’s high-speed railways is highly variable, and the traction power supply system installed along the tracks exhibits diverse comploutageies over spatial and temporal scales. Since its commissioning, the traction power supply system, which has been continuously in service status, needs to withstand the changes of the four natural seasons and occasionally suffers from the devastating impacts of lightning, rain, snow, and strong winds. Covering more than 30 provinces and cities, the high-speed railway network shows significant spatial variability, especially for individual high-speed railways lines that exceed 1000 kilometers in travel distance, along which the traction power supply system spans multiple regions and natural climate zones, potentially experiencing different environmental impacts at the same time, such as the Beijing-Harbin railway reaching cold regions and the Lanzhou-Xinjiang railway crossing two major wind zones. The complex and variable external service environment poses considerable challenges in establishing a unified risk assessment model for the entire line’s traction power supply system. Additionally, the internal service environment of the traction power supply system is equally complex. According to the different transport capacity requirements and train operation schedules from origin to destination across regions, the density of traffic varies from section to section, causing diverse impacts on the traction substation equipment due to varying traction load characteristics. Moreover, due to the different characteristics of regional power grids, including adequacy, power supply capacity, and power quality, the reliability of the external power source for the high-speed railway traction power supply system also varies. Therefore, most existing studies focus on analyzing the reliability of power supply equipment, traction substation connections to the power system, and capacity configurations individually. This approach leads to assessment results that only reflect a single aspect of security risk and fail to evaluate the overall risks faced by the traction power supply equipment or the system as a whole. To ensure the safe, reliable, and continuous operation of high-speed railways, the traction power supply system requires extremely high operational reliability. Traction power supply equipment, such as traction transformers and circuit breakers, is the core component of the high-speed railway traction power supply system, and its safety and reliability are critically important for the normal operation of the entire high-speed railway. Additionally, the reliability and risk assessment of traction power supply equipment provide a basis for operational maintenance decisions and are key topics in current research on traction power supply system maintenance technology.