In order to acquire migration and interaction laws of smoke with inert gas in the process of inert gas injection in fire zone sealing of mine, two full-scale experiments on inert gas injection in fire zone were been conducted in the ambulance brigade of Hegang branch of Heilongjiang Longmay Mining Holding Group. The experiments continuously detected temperature, gas concentration, velocity, etc. in the experimental tunnel with beam tube detection, bladder detection, and thermal infrared analysis. The results indicate that the stratified distribution of combustible gas in the fire zone sealing of mine is obvious. The lower the gas concentration is, the more obvious the gas stratification is. Injected turbulence inert gas “disturbs” the laminar flow condition of combustible gas in the closed zone, thus weakening the stratification of combustible gas. In addition, the dilution effect of nitrogen injection on combustible gas layer is related to distance of the combustible gas layer from nitrogen injection port. Inert gas injected to the fire zone sealing will promote combustible gas layer in the fire zone sealing to migrate towards air intake side like gas piston. Thus, the combustible gas layer flows to fire source owing to piston action of inert gas injection. It is the reason of explosion at the initial stage of inert gas injection. The dilution effect of inert gas injection on middle and lower part of combustible gas layer is better than that of the upper part. Explosion hazard exists at initial period of inert gas injection.