In order to solve the problems such as the danger，the integrity of the train structure and the safety of personnel when the high-speed train was operated in a low-vacuum tunnel，the temperature attenuation characteristics of the high-speed train compartment in a low-vacuum tunnel in a fire were explored by numerical simulation. Then the temperature distribution inside the adjacent carriages was analyzed. Finally，the distribution characteristics of the maximum temperature inside the burning carriage were studied. The results show that the temperature of the burning carriage and adjacent carriage roof decreases exponentially along the longitudinal direction. In adjacent compartments，the power has an effect on temperature attenuation. At low fire source power (0.3-0.6 MW)，the high temperature smoke spread is relatively weak，and passengers in the adjacent carriages are relatively safe. At medium source power (0.7-1.1 MW)，the high temperature smoke spreading is significant，and the temperature abrupt point appears due to the influence of carriage wall and door. At high fire source power (1.2-1.5 MW)，the heat plume intensity is higher，and high temperature smoke spread is relatively less affected by carriage wall and door，and temperature spreading trend in the connecting part of carriage is basically the same as that in the adjacent carriage. The maximum temperature in the carriage is related to power of fire source and distance from fire source to the ceiling，and there is a linear relationship.