Abstract: The collapse problem of coal seam drilling hole which restricts the efficiency of gas drainage and seriously affects the safety of coal production. Studying the damage zone radius of coal body drilling has important significance for solving the collapse hole problems of coal seam hole drainage. Tests were carried out to determine the basic mechanical parameters of 4 kinds of coal samples, which were measured by uniaxial compression, Brazil splitting and firmness coefficient; and the basic mechanical parameters of coal samples were obtained. Based on this, we established the mechanical model of coal seam drilling, the numerical analysis of the influence of ground stress, lateral pressure coefficient and firmness coefficient on coal seam drilling damage zone radius. The study shows that the radius of vertical direction of coal drilling damage zone decreases and the horizontal direction increases gradually with the increase of ground stress; with the increase of lateral pressure coefficient, the vertical damage radius increases gradually, the horizontal direction decreases gradually; with the increase of coal firmness coefficient, the drilling damage zone radius decreases gradually.