Abstract:The regular behavior of weighting and caving of well-layered strata around coal face,with many thin overlying layers,is studied,and the rock pressure caused by the caving is relatively easy to control. But the caving and rock pressure of very thick sand overlying strata,the thick key strata,is very complicated and needs further study. The breakage and collapse of thick key strata(super thick roof of sand rock ) around coal face,with real geological conditions from a coal mine borehole columnar section,is studied by a computer grogram,rock fracture process analysis(RFPA). The results show that there are basic differences of the breakage and collapse between thick key strata and thin strata (or long beams). The shape of the first breakage and collapse of thick key strata is an arch,and the periodic breakage and collapse is in short blocks with different lengths. The roof of thick key strata weights stochastically,and the effects on the coal face support are different. The sliding of large blocks,which is the most dangerous of rock weighting to the support observed in this paper,is a new and severe challenge to the rock pressure control. The results can provide theoretical reference for mining design and strata control.