Abstract: In order to solve problem of the secondary disaster caused by the goaf gas pressed into the fire area when the method of pressure balancing ventilation is used to prevent the harmful gas of upper fire area discharge in the fully mechanized caving surface under large vertical distance fire area, by using the method of theoretical research, the control condition of flow field balance in double-layer goaf with large vertical distance is analyzed, and the safe adjustment interval of flow field balance in double-layer goaf is determined. It is applied in the western 8101 working face of Tongxin Coal Mine, and the results show that, when the gauge pressure difference of U-shaped water column connecting the double-layer goaf meets (350+0.016l,538+0.016l),l∈(85,1 600), the volume fraction of CO at the corner of the working face is always kept below 24×10^-6 during the mining period, which effectively guarantees the safe mining of the working face.