Abstract: On the basis of deformation mechanics,the paper promotes FEM program for the displacement and strain calculation of elastic,homogenous rock layers under mining,and realizes the coupling analysis of large deformation strain and fissure net permeability according to relations between displacement of rock layer and breadth of fissure.There is a model analysis and calculation for the change of fissure permeability of roof rock layers under mining.The results show that vertical fissure permeability increases about 4 times,and horizontal one decreases about 4 times under the condition of non-considering roof rock layers break.That is to say,the deformation in roof rock layer have a great influence on the fissure permeability.