Abstract: A coupling relationship between the gas pressure and the coal deformation is obtained based on the principle of effective stress. Under joint actions of the crustal stress and the gas pressure, in the coal there will be elastic-brittle damages and layer fractured-powdering damages, accordingly, and the danger of coal and gas outburst is estimated. A three-dimensional model is validated by the numerical simulation result, which is approximately in agreement with the outburst experiment in the coal shockwave tube.