Abstract: To meet the need of applying the technology of layer separation grouting to slow down the surface subsidence,we study the law of the asynchronous bend of rock layers resuled in the layer separation.Based on the elastic theory,the deformation character of the layer separation is studied under the hypothesis that rock layers are treated as rock plate. Mechanical model for flexibility of rock boards is founded. The model factually reflects the deformation of rock boards under the action of the horizontal stress and self weight in essence. The model can be used to calculate the flexibility of the rock layers where layer separation grouting produce a condition of layer separation in ground. And the obtained result will provide a theoretical basis for the application of layer separation grouting to slow down the subsidence. 