Abstract: In order to inspect the influences of gas seepage on the outburst of coal and gas, a set of device was made. The device includes coal sample cell, simulated roadway, device for compaction of coal sample, gas injection system and gas pressure measuring system. Several sample cells were assembled to observe the gas pressure gradient and ensure the same compactness of all coal samples. The grain size of coal samples was smaller than 4.75 mm. Coal samples were compacted at 15 MPa. The inner diameter of sample cell is 199 mm and its length is 1 000 mm. Ball valve was made as uncovering coal apparatus and its inner diameter is 40 mm. No axial pressure was loaded on coal samples during tests. The uncovering coal tests showed that the critical gas pressure gradient was 3.12 MPa/m. From the view of permeation in stability of coal containing gas, the process of the holes with small mouth and big belly as well as the principle of controlling outburst measures were analyzed.