Abstract: China's coal mines are mostly low-permeability, high gas mines, and due to low permeability coal, gas extraction and control is difficult. SEM analysis of coal samples microstructure can observed intuitively microscopic coal pores, voids, cracks(fissures) development, distribution, connectivity of the pore structure, can provide the basis for taking improvement coal permeability measueres and coal seam gas control. Through detailed observations in No.12 Coal Mine, it can be found that the surface contains large amounts of 200 to 3 500 μm long, 1 to 20μm wide cracks in the structure, in addition to a considerable number of cross-sectional area for the 10 to 20 μm² pore diameter of the structure and a certain number of 100 to 200 μm pore structure. It also observed that these holes also had connectedness between joints. Overall, the pores, cracks in No.12 Coal Mine coal samples are well developed with better connectivity between holes. In addition, this study observed three clay minerals in coal samples, namely montmorillonite (irregular flakes), kaolinite (hexagonal plates) and illite(floc), these clay minerals has the characteristics of a rapid expansion with water, which should be noted in gas control process.