Ensuring the safety of the on-fire train moving in a subway tunnel is the goal of the corresponding emer- gency rescue.In this paper,with the help of STAR-CCM + possessing the function of mesh sliding,CFD (Com- putational Fluid Dynamics) simulations are carried out to investigate the effects of train speed and heat release rate on the smoke characteristics in a tunnel,and the distribution of smoke temperature as well as the optimal speed of the on-fire train traveling in the tunnel are explored.The results show that (1) for the on-fire train moving in a subway tunnel，there is an optimal speed corresponding to the lowest temperature,namely 50 km/h; (2) when the train moves at a constant speed,the temperature peak at the typical eye points increases with the heat release rate; (3) at a constant heat release rate,the maximum temperature first decreases and then increases with the train speed,presenting an upward parabola; (4) the temperature at the train roof inlet gradually increases when the on-fire train moves forward in the tunnel,and the maximum temperature is of a large oscillation on the neutral surface; (5) the minimum temperature (166. 45 ℃) occurs at 340 m in the tunnel; and (6) the train might be burnt due to the high temperature at the train top,so that a ventilation measure should be adopted to reduce the temperature of the annular tunnel space when a subway train is on fire.