Based on flexure theory and inharmonic relationship of deformation of rocks

the criterion of hard roof separation was built. And the influence of homologous parameters on roof deformation was given. Using the technology of telemeter measurement to monitor rock separator in goaf

the conclusion can indicate: the system of telemeter can monitor effectively the separation information of roof rock. By anglicizing the curve monitored

the position of roof where separation happens can be confirmed; and the thickness of cave of roof would be predicted. Using the information monitored by the system of telemeter before roof cave

some prevention can be practiced to protect the safety mining under hard roof.