Abstract: In order to further study the theory and technology of gas disaster at the horizontal section of steeply inclined thick coal seam, analyzing and making summary of the working surface gas gushing source, calculating gas concentration distribution at the working surface, measuring the gas emission quantity at mined out area by the method of source and estimation, obtaining the gas concentration distribution law along the length of the working surface and the direction of the vertical section. The research shows that the gas concentration at the working face increases gradually along the airflow direction, uneven distribution along the working surface vertical section, the gas concentration at the mined out area higher than coal wall with the effect of mined out gas emission, gas drainage and airflow. Considering the effect of gas drainage, The amount of gas emission in the mined out area accounts for 85.08% of the gas emission at the working face. Therefore, comprehensive measures are suggested to prevent gas disasters by the mining method of the mine out area and adjacent layer or lower coal pressure reduction during mining process.