According to a large number of drilling and underground mining expose data of the third level west wing No.戊8 coal seam in No. 6 Mine of Tian'an Mining Industry, the coal seam situation was studied and analyzed, the coal seam with simple structure, becomes stripped and thick from west to east. Combined with geological condition of No. 6 Mine, Guodishan fault and Jiaxian fault caused by crustal uneven subsidence is the main reason of the west wing No. 8 coal seam variation.