Abstract: In order to study the characteristics of smoke flow when fire occurs in underground coal mines, and then accurately analyze the state of smoke flow, the flow state of the flue gas in the natural state at 10 s is simulated in this paper to determine the approximate stage of the ignition and smoke production, which is used as a reference for the subsequent experiments; the 3-dimensional particle image velocimetry (3DPIV) was utilized to photograph the open, closed and sealed conditions of the tunnel, and the start/stop control of the fan with a fixed wind speed of 1 m/s was combined to study the motion of the smoke flow under different conditions. The results show that: the open smoke flow of the roadway is relatively simple, and once the roadway is closed, the smoke cannot be diffused, and complex flow changes will occur in high concentration of smoke, such as laminar flow, excessive flow, turbulence, countercurrent and bifurcation of the smoke flow, etc. When the roadway is closed and sealed, the smoke flow "gushing" will occur. At this moment, the flow state of the smoke flow is complex and changeable, but the smoke flow will be stable after a certain period of time.