Abstract: To investigate the propagation characteristics of gas explosion under complex conditions of coal mine tunnels, the effect of tunnel section mutation on pressure, temperature, flame propagation and velocity in the process of gas explosion was examined by FLACS simulation. The results show that the pressure peak and temperature peak of measuring points were obviously higher when the tunnel section was mutated. With the sudden expansion of cross-sectional area expanding in tunnel, the area of flame peak surface became larger while the speed of flame propagation got slower. Conversely, with the sudden contraction of cross-sectional area shrinking in tunnel, the more pronounced turbulence occurred when flame propagated to a sudden contraction section, which speeded up flame propagation. Simultaneously, the flame peak area was stretched. In addition, the turbulence intensity of air flow was increased by the cross section mutation of tunnel, which speeded up the reaction rate of explosion. Accordingly, flame propagation in the tunnel with cross section mutation was faster than that in the tunnel with unchanged cross section.