The train fire has been greatly focused by fire researchers all over the world, the key to which is the study of smoke flow. The simulation model is set up to analyze the concentration and the temperature of smoke flow during the train carriage fire. The concentration and temperature is very high near the fire in the closed space. Meanwhile, the spreading speed of smoke flow will be accelerated when the doors are open. The concentration of smoke near the fire will be decreased. The simulation shows that the fire should be extinguished at the initial stage. After being developed because of the pouring of fresh air, the smoke concentration and the temporary ventilation should be controlled.