Abstract: The complexity of safe mining arised from two aspects due to excavation disturbed zone(EDZ) underneath water.One was the re-distributed ground stress;whilst the other was the dynamic behaviour of a mining-rock mass system,and damages were closely related to the mining process and time dependent.The cracks and damage of overburden rock-mass in the large scale mined-out area(LSMA) were not only the direct and instant response but also the accumulated dynamic response of a rock mass disturbed by mining activities.Based on in-situ experiment and analysis,the dynamic destabilization of the large scale mined-out area(LSMA) and ground subsidence were determined quantitatively;whilst the safe mining and the induced environmental hazard were comprehensively evaluated in the excavation disturbed zone.Under the condition of preserving the existing river and using the present mining method,the lagged reserves had been mined successfully.