Abstract: In order to set up the distinguishing criterion of the seam smoldering state in the mine gateway, a seam smoldering simulation experiment device of mine gateway was designed and manufactured.The simulation experiment device was applied to study the length of the natural air flow zone at the gateway entry when the s eam smoldering was stably spreading, the length of the heat air vortex zone in the smoldering face, the max allowed distance between the natural air flow zone and the heat air vortex zone and the limit distance between the smoldering face and the gateway entry. Based on the circumstance, the distance cofficient m between the smol dering face and the gateway entry when the seam was in smoldering as well as the limit distance coefficient m0 between the smoldering face and gateway entry when t he seam smoldering was stably spreading in the gateway were provided.When msm0, the smoldering would be spreading in stable and when m>m0, the smoldering wo uld be gradually extinguished.The experiment measured that m0 = 142.33 m-1 when the lignite smoldering was spreading in stable in the gateway.The experiment resul ts showed that the m and m0 as the distinguishing criterion of the seam smoldering state would be rational.