Abstract: Aiming at the range of the goaf of mechanized coal mining operation face, using three-dimensional numerical simulation technology and taking the Y-type ventilation method of the 1205 working face of Dongrui Coal Mine as the research object, the distribution characteristics of the gas flow field in the goaf before and after the extraction operation are analyzed, and the simulation data are compared and verified with the experimental observation data.The results of the study show that: before extraction, after the Y-type ventilation is adopted, the distance between the goaf of the mechanized coal mining face in the strike direction and the working face gradually increases, and the gas concentration in the deep part of the area shows an increasing trend, i.e.,the maximum value of the gas concentration(peak volume fraction)is 98.6%,and in the tendency direction the gas concentration in the working face is relatively low, which is not more than 1.0%;after extraction, the mechanized mining face goaf's maximum volume fraction of gas was reduced to 4.6%,and more than 75% of the area in the goaf had a gas volume fraction of 3.0% or less, and the volume fraction of gas in the mechanized mining face and its upper corner area had a gas volume fraction of 1.0% or less, which was a significant reduction of the gas concentration.