The experiments of outburst coal’s gas seepage are carried out by triaxial permeameter which is independently developed. Under the condition of fixed gas pressure, different confining pressures and axial pressures acting on raw coal test samples are tested. It shows that as the increasing of confining pressure, coal sample seepage velocity tends to decline, and this phenomenon is more obvious for the coal with serious original injury. The relationship between seepage velocity and confining pressure can be described as a quadratic function，and its general expression is established. Coal sample’s seepage velocity-strain path is similar to stress-strain path, therefore, the changes in coal seepage velocity indirectly reflects the process of the evolvement of coal damage. The influence of effective stress on coal sample seepage velocity can be concluded as hypersensitive stage and smooth stage, and in the hypersensitive stage, seepage velocity of the coal sample vary quickly, while in smooth stage, its variety is not obvious. In different stress conditions, the degree of development for hole and cranny of coal affect coal gas energy and elastic deformation energy in coal body as well as the form of coal destruction.