Abstract: Taking the anomaly of dredging and draining water in the Jining No.2 coalmine as an example, this study predicts the development position of bed separation in the discriminant formula based on the composed rock beam theory, simulates the dynamic development process and distribution regularity of bed separation using discrete element software UDEC, and probe the position and spread of bed separation through 3D seismic.The result shows that the maximum bed separation developed in the larger gap between mudstone and middle-fine sandstone after the working face completed, the distance between the gap and coal seam is 60 m approximately.Based on the elastic thin plate theory, the study predicts the volume of bed separation by calculating the difference of deflection between upper and down rock plate.The predictive value can be used as the maximum total volume of bed separation developed in seam roof.