Abstract: Based on blockiness and the matter-element extension theory,this article introduces BET method(classification method based on blockiness and the extension theory) especially suitable for roof stability analysis. The integrity of roof rock was reflected by blockiness in three-dimensional space,and an evaluation system was constructed with blockiness,uniaxial compressive strength,joint condition and groundwater condition as evaluating indicators. The classical domain,the segment and the object element of the model were established,the incompatible problems between these indexes were analyzed,and the index weights were calculated by the extension method. After the correlation degree was comprehensively calculated,the stability classification method and standard were determined. Selecting four test areas of fractured rock mass in Guangxi Tongkeng Mine,an engineering application study of BET classification method was carried out. The results of traditional classification methods,such as RMR method,RSR method and Q method,were respectively compared to that of BET method. It is shown that compared with these traditional classification methods,the index system selected by BET method is more comprehensive and its evaluation method is more objective and scientific.