According to the occurrence and mining conditions of 9 # and 10 # coal seams in Wuhushan mine,the distribution of floor stress caused by mining upper coal seam was researched with numerical simulation,the effect of the horizontal floor stress of upper coal seam on the mining gateway of the lower ultra - close coal seam under mined - out area was analyzed. The result of study showed that the so - called " stress - relaxed area" in the edge of mined - out area is only to the vertical stress,but it is not horizontal stress - relaxed area. The place where the vertical stress is minimal but the horizontal stress is maximal,the place where the vertical stress is maximal minimal but the horizontal stress is minimal. The vertical stress and the horizontal stress tend towards stability at the place where is 20 meters away from the coal wall of mined - out area. If mining gateway is laid out in area of stable stress,the deformation of wall rock of gateway comes to last,it is favourable to the gateway drive and its mainte- nance.