Abstract: Based on the condition of the nearly flat coal seam of Bulianta Coal Mine, the results from numerical tests of modern coal mining under different structural medium with the numerical simulation program FLAC^3D, show that under the mining of the same intensity, hard cover rocks have stronger ability to resist deformation, so the influence of the working face safety mining and the surface is relatively weaker; whereas, flexible cover rocks have weaker ability to resist deformation; the sand inrush and water inrush in the working face occur easily; the influence of the working face safety mining and the surface is relatively stronger; when hard cover rocks are nearer from the working face, coal mining has larger influence on cover rocks.