In the light of the mining conditions of Shangyuquan coal mine, the three dimensional finite difference method was adopted to simulate and analyze the failure features and stress distribution of side wall rock affected by extracting activity where was at front or back some distance from the coal caving face of which the advance reached 150m. According to that, the width of coal pillar protecting sublevel roadway should be determined as 16 - 20m for the fully -mechanized sublevel coal caving of No. 10 coal seam in Shangyuquan coal mine.