Abstract: In order to study the width of waterproof coal and rock pillar of stepped fault group，the stepped fault group composed of F23 fault and SF27 fault in Xingdong Mine of Hanxing Mining Area was taken as the research object. According to the deformation and failure depth of floor rock layer caused by coal seam mining，the calculation formula of plastic zone failure width of waterproof coal and rock pillar of stepped fault was deduced by using the stability structural mechanics model of fault quadrilateral water⁃ proof coal and rock pillar，according to the stress and geometric characteristics of local rock mass in quadri⁃ lateral coal and rock pillar. The calculation results are consistent with the results of similar simulation ex⁃ periments. Combined with the results of previous graben fault coal pillar retention，it shows that the model has good applicability for the study of fault group waterproof coal pillar retention.

Key words: step fault, waterproof coal rock pillar, plastic zone, floor failure depth