Abstract: The strata and surface movements resulting from underground mining can cause the surface water in the mining range to burst into the underground, which threaten the safety of the production in coal mines. Therefore, to research the overburden's failure laws, especially the height of water flowing fractured zone, is extremely importance. Fast Lagrangian analysis is a new numerical analysis method in resent years, this article attempts to use it in the prediction of the height of caving zone and water flowing fractured zone in fully mechanized caving mining based on a coal mine in Shanxi Province. Compared the results of numerical simulation to numerical calculation of empirical formula and measured values, then the feasibility of FLAC which used to predict the height of caving zone and water flowing fractured zone is demonstrated.