Abstract: Observations have been made for a long time and in a wide range on deformation and failure of floor strata of deep tunnels. Floor strata movement, front abutment stress and floor rock osmosis were observed. Based on data of displacement observed and statistical data of in-situ rock stress, back analysis of displacements is made to obtain the elastic moduli of rock mass and the abutment stress. It was found that the elastic modulus of the rock mass is 0.445 times the data from laboratory test of its sample and the front abutment stress is 1.7 times the stress in-situ rock mass in the vertical direction. Stress distribution of the floor rock mass and the range of disturbance in floor rock affected by mining are discussed.