A commercial software package FLUENT is used for numerical simulation of the distribution of the air flow and gas in goaf of the working face with downward ventilation. With the increase of coal seam inclination, the phenomenon of airflow stagnant appears first on the upper part of the goaf, then backflow starts and eddy forms a certain distance away from the working face. When the coal seam slope increases to a certain angle, the air leakage in working face entirely reverses and flows into the gob from the bottom part of the mining face, and returns to working face from the upper part, particularly the upper corner of the working face. As the coal seam angle increases, the natural ventilation pressure in goaf increases too. When the natural ventilation pressure is less than the ventilation pressure differential in working face, the bigger of coal seam angle, the smaller of leakage air volume, and the closer of high-concentration gas migrate from goaf to working face. When the natural ventilation pressure in goaf is greater than the ventilation pressure differential in working face, with the increase of coal seam angle, the natural ventilation pressure and the air leakage volume increases, the range of leakage air backflow increases, high-concentration methane in the goaf will move to deep and total amount of gas in goaf decreases.