On the basis of suitable arrangement for the special stress surrounding and parameters selection, Realistic Failure Process Analysis 2-D (RFPA2D) numerical simulation of extra-thick coal seams’ displacement and failure is carried out. It’s proved that the numerical simulation results are consistent with the in-sit measurement results of top coal’s advance supporting stress and deep-hole displacement. So application of RFPA2D in sub-level caving mining extra-thick coal seams is reliable. It’s also proved that application of RFPA2D in sub-level caving mining can do great help to study the nature of top coal’s displacement, fragmentation and failure process of extra-thick coal seams. As the top coal’s displacement and failure situation under certain circumstance can be forecasted by RFPA2D numerical simulation, the most suitable top coal thickness under certain circumstance can be predicted by RFPA2D numerical simulation test, which can do great benefit to extra-thick coal seams’ safe and high efficient mining.