1.Key Laboratory of Deep Coal Resource Mining Under Ministry of Education of China，China University of Mining and Technology，Xuzhou ，China;2.School of Mines，China University of Mining and Technology，Xuzhou ，China;3.Datong Coal Mine Co.,Ltd.,Datong ，China

In terms of the characteristic that the phenomenon of major cycle and strong strata behavior was prone to appear in the mining extremely thick coal seam of large space stope in Datong Coalfield，the theoretical analysis and field measurement were adopted to study the structural breakage of far field stratum in large space stope and its influential mechanism on strata behaviors.The “triangle plate” structural mechanics model for far field key stratum broken in the shape of “horizontal O-X” at large space stope was proposed initially，and analyzed its dynamic instability process.It was indicated that the instability of the “triangle plate” structure of far field key stratum was the primary reason for the phenomenon of major cycle and strong strata behavior，which was verified by the mining practice of extremely thick coal seam in Datong Coalfield.In addition，the phenomenon of the far field key stratum breakage induced strata behaviors also occurred in Shendong Coalfield，and its “horizontal O-X” breakage features were verified by the form of mining-induced fissures on ground.The research results can provide guidance to the scientific control of strong strata behaviors in large space stope.