Abstract: Regarding the thermal reliability of the main circuit breaker of high-speed rail EMUs under large temperature differences environments, research based on digital twin technology is conducted. A five-dimensional model architecture and implementation framework for the digital twin of the main circuit breaker are constructed. By integrating multi-physics field simulation software with on-site monitoring data, geometric modeling and thermal field analysis are performed. The influence of environmental temperature on the temperature distribution of the contact current heating field under large temperature difference conditions is analyzed in detail, along with the mechanism of interaction between train running wind speed and environmental temperature on heat dissipation. The research demonstrates that digital twin technology can accurately simulate the dynamic characteristics of thermal coupling; the temperature field is distributed in a gradient centered on the contact, and the environmental temperature determines the fundamental temperature rise level. An increase in train running wind speed can significantly enhance convective heat dissipation, and this effect is more critical in high-temperature environments for suppressing the temperature rise of the contact. Theoretical support is provided for the design of temperature difference resistance, heat dissipation optimization, and fault early warning of the main circuit breaker, with the engineering application of digital twin technology in the thermal characteristic analysis of high-voltage equipment in rail transit being promoted.