Abstract: In order to analyze the influence law of ground pre-extraction effect of CBM, Comsol numerical simulation software was adopted to carry on numerical simulation research on ground pre-extraction of CBM under different geostress and reservoir pressure conditions. The results show that with the increase of geostress in coal seam, the porosity of matrix decreases and cracks tend to close, as a result, the permeability of coal seam decreases, which reduces the percolation rate of gas in pores and fractures, and finally leads to the decline of gas production rate and gas production volume; reservoir pressure is positively correlated with CBM production rate, the higher the reservoir pressure, the higher the gas production rate, and the higher the cumulative gas production; with the increase of gas extraction time, the permeability of coal seam increases gradually, and the change of permeability of coal seam becomes more obvious with the increase of reservoir pressure.