Abstract: According to the air leakage problem of the goaf increased by the gas drainages in coal mining face, neighboring seam or goaf, taking the tail gateway of No.401 coal mining face in Tianchi Mine to drain the gas in goaf in combination with the high level gateway along the roof strike to drain the gas in top neighbor seam a nd the borehole in along seam to drain the gas in the mining seam as a case of 3D gas drainage system, a site measurement and simulation method was applied to stu dy the air leakage law of goaf under the 3D gas drainage system.The study showed that under the role of the 3D gas drainage, the depth of the air leakage flow into the goaf would be highly increased and the role of the high level gateway could make the air leakage value of the goaf increased and could cause the spontaneous combus tion danger of the coal left in the middle section of the goaf increased.