Abstract: In order to solve the mutual contradiction of the two evaluation indexes between the seam permeability cofficient and the attenuation factor of borehole gas flow during the judgment of the difficult degree for the seam gas drainage and to solve the mutual comparison problems of the different seam gas drainage difficult degree, taking the Mine Gas Drainage Regulations as the basis, based on the extenics as the theory, the classics area and sectional area was determined to evaluate t he seam gas drainage difficult degree and a general formula was obtained to evaluate the seam and each grade relevance.The application results showed that the appli cation of the extenics method to evaluate the seam gas drainage difficult degree and to compare the gas drainage difficult degree of different seam would be feasible.