Abstract: In order to find principle of coal seam gas occurrence under influence of single graben structure,graben structure and coal seam occurrence characters of Gucheng coal mine in Shanxi province were analyzed,different gas geological element for north and south side of graden were confirmed,and then field testing and mathematics method were applied,and No.3 coal seam gas occurrence principle was analyzed,obtained that gas content increased with coal seam buried depth increased,appeared obviously linear law as W=0.0151H+5.0224,W=0.0439H-14.163,gas content was tested in field during roadway driving,and gas content of No.3 coal seam of the mine was predicted,the results showed that deviation between predicted value and actual value less than 5%,so it could be used to predicted gas content.