During a fire in a high-speed train carriage, window breakage can create lateral openings, significantly affecting combustion behavior and temperature distribution. This study employed a combination of 1∶8 scaled model experiments and numerical simulations to investigate the influence of different opening positions on fire evolution inside the carriage. Additionally, it quantitatively analyzes the combined effects of opening position and heat release rate on flame propagation speed and longitudinal temperature attenuation. The results show that, for all opening positions, as the heat release rate increases, fire evolution and smoke/flame behavior at the openings undergo three distinct stages: (1) a fully developed combustion stage, (2) an oxygen-deficient combustion stage, and (3) a continuous overflow stage. The maximum internal temperature exhibits three trends with increasing heat release rate: an initial rise, followed by a gradual decline, and finally a sharp decrease, corresponding directly to fire development patterns within the carriage. The study further examines the effects of heat release rate and opening position on flame propagation speed and proposes a predictive formula for flame movement. The findings show that when the heat release rate is 50.80 kW, the opening position has minimal impact on flame propagation speed. However, when the heat release rate exceeds 50.80 kW, flame speed at opening position 2-4 decreases as the distance between the opening and the fire source increases, while opening position 1 exhibits the slowest flame propagation. Additionally, the study analyzed the maximum internal temperature and the temperature attenuation patterns on both sides of the openings, and established a predictive model for temperature attenuation at different opening positions in high-speed train carriage fires. The research findings provide valuable insights for fire prevention and mitigation strategies in high-speed train carriages.