To reveal the flame propagation behaviors during coal dust explosions, a kind of coal dust cloud was studied through experiment and numerical simulation in semi-enclosed vertical combustion tubes with different lengths. A high speed video camera and a thermal infrared imaging device were used to record the flame propagation process. The result indicated that the supreme flame propagation velocity and the highest flame temperature both rose gradually with the tube length increasing. Meanwhile, FLUENT was applied to numerical simulation of flame propagation behaviors during the coal dust explosions. The simulation result showed the flame combustion and the temperature varying process was consistent with the experimental result. It also revealed the distribution of flow velocity in the flow field during the combustion process, which indicated that flow velocity higher than flame propagation velocity was an important reason for dust re-entrainment and consistent explosion. (C) 2014 Elsevier B.V. All rights reserved.