Abstract: In order to ensure the outburst prevention effect of a joint mining with a underneath protective seam and the surrounding rock with long distance and ultr a thin and to reduce the outburst prevention cost and many other problems occurred from the over mining of the seam and surrounding rock, taking Zhongtai Company as an example, with the analysis on the factors of the protective seam No. 1-8 seam mining with a long distance and ultra tine affected to the protective effect of No. 2-1 seam, the location of No.2-1 seam in " caving zone, fracture zone, bending subsidence zone" was calculated under the deferent mining height in No.1-8 seam. The RF PA2 Dwas applied to simulate the deformation condition of No. 2-1 seam when the mining height of the lower protective seam was 0.5 m, 1 m and 1. 5 m. In combined with the results of the theoretical analysis and simulation, when the mining height of the protective seam was determined as 1 m, the permeability coefficient of No.2-1 seam would be increased by 106 times and the max swelling deformation value would be 0.613%.The site experiment showed that when the mining height of the coal m ining face in No. 1-8 seam was 1 m, the gas drainage volume from the mining seam within the protected scope of No.2-1 seam was reached at 14 m3/min, the max resi dual gas content of the seam would be only 1.83 m3/t and the protected seam had an excellent regional outburst prevention effect.