Abstract: In order to understand the change law of gas concentration in simultaneous extraction of coal and gas. This paper using similar simulation and numerical analysis to calculate the stress of roof displacement and plastic area. The conclusions are as follows: While the 6# coal mine was advancing, the pressure relief range of floor, vertical displacement and the depth of plastic failure area are increasing with the working face advancing. While the working face are advanced at 80m, the pressure relief range of floor arrived 60m and tended to be stable,the vertical displacement arrived at 90mm and tended to be stable, the depth of plastic failure area arrived at 20m and tended to be stable.The advancing of 6# coal seam are in sphere of action of 6# coal advancing. The vertical stress in top are small and part area appears zero of stress，the height of pressure relief in top increased. The plastic failure area in 6# coal is larger than 6#coal seam. The maximum gas concentration during drilling of the 6# coal seam is 23% higher than that of the 4# coal seam, and the gas concentration of the drilled hole is still 10% higher than that of the 4# coal seam after the compaction is stable in the goaf. After the second mining pressure relief can significantly improve the drainage effect.