To further study the gas-coal dust explosion hazards under complex conditions. Experiments were conducted in pipe-line systems containing explosive pipe-line and pressure relief pipe-line. The effect of coal dust concentration and particle size on the flame dynamics of gas-coal dust explosion was investigated. The flame structure in the explosion pipe-line is divided into two-stages: spherical and round-finger. In the pressure relief pipe-line, the flame structure e varies at working conditions. Flame front position increases with time, showing a class exponential growth trend. The flame front velocity increases in the explosion pipe-line, has a short drop during the entry into the pressure relief pipe-line, and then increases. With the increase of coal dust concentration, flame propagation time has been increasing in the pipe-line system and the explosion pipe-line, with the shortest time at 25 g/m³. Flame propagation time first increases and then decreases in the pressure relief pipe-line, the shortest time at 50 g/m³. The maximum flame front velocity first increases and then decreases. The maximum flame front velocity is maximized at 50 g/m³. With the increase of coal dust particle size, flame propagation time has been increasing in the pipe-line system, and in the explosion pipe-line, flame propagation times have been decreasing in the pressure relief pipe-line. The maximum flame front velocity first increases, then decrease, and increases again. The maximum flame front velocity is minimal at 45 μm.