Abstract: By using FLAC^3D simulation software, the numerical simulation of pressure relief gas drainage was carried out in steeply inclined thick coal seam mining process of Dahuangshan Coal Mine, and the stress distribution and displacement laws of roof and floor of two layers of coal was obtained. We analyze the coal and rock stress characteristics of the coal seam floor in the middle and large slots working face. It is necessary to carry out gas pre-extraction and pressure relief gas drainage. According to the measured data in field, the residual gas pressure of the replacing working surface is 0.21 MPa, the residual gas content is 2.873 m³/t, and the amount of gas can be desorbed is 0.563 m³/t, which can determine that the gas drainage effect in this area is up to the standard.