Abstract: In order to further study the process of coal and gas outburst, the stress states were analyzed for the original stress region, the stress concentration region and the pressure relief region in front of the uncovering coal face. Effective stress expressions were deduced for the regions. And the effective stress expressions were verified by using the numerical simulation method of PFC^3D, FLAC^3D program. The results show that the calculation results of the effective stress are close to the theoretical results, that there is a cubic polynomial correlation between the effective stress values and distance from uncovering coal face, that the outburst region rapidly expands at first and then steadily increases in the process of coal and gas outburst, that the outburst region is a hole with a small mouth a large cavity, and that the crack propagation process of coal and rock mass are divided into three stages, and the growth rate of number of cracks increases at first and then decreases at each stage.

Key words: coal and gas outburst, effective stress, numerical simulation, crack propagation, outburst region