Abstract：Based on the engineering background of No.8402 stope in Silaogou coal mine of Datong miner bureau，considering the surrounding rock structure in the stope and mechanical property in rock bodies with various kinds of homogeneous joint planes，an assumption that key roof is divided into a series of interacting rectangular rock plates is presented，then according to the thickness of key roof and its material characteristics，a mechanical model of elastic thin plate group is set up. The deflection and the stress of the model are analyzed by the finite element analysis software ANSYS. After comparison between the results from numerical modeling and those from field engineering，the following rules are generalized：(1) along the stope，the rock plate with relatively small ultimate strength breaks first，(2) for the load transfers and the supporting boundary becomes adverse，the adjacent plates break in turn during the advance of the stope，the rest may be deduced by analogy，and (3) key roof will break up to the two ends of the stope. At the same time，the phenomenon that resistance in middle bearer is larger than those at the two ends is fairly explained，and an appropriate reason is given to explain the phenomenon that mine pressure in the surrounding rock is relatively big and accompanies a relatively intense phenomenon when the key rock breaks in the stope from the view of material characteristics.
