Karst caves are the significant feature in carbonate rocks. To determine whether a reservoirs develop or not in and around karstic caves, it is a key to know the existence of buried collapses under overlying load. The principle of rock mechanics for indicates that the buried collapses of karst caves are under control of three key parameters, i.e. the anti-bending strength of rock, the cave scale and the distance of a cave away from the exposed weathering surface. According to this principle, quantitative formulas and a plate of buried collapse depth of karst cave are obtained. Actual drilling data from Ordovician limestone caves in Tarim Basin prove the correctness of this conclusion and the plates of buried collapse depth can be applied in forecasting of collapsed caves present underground, an accurate burial evolution history of caves and evaluation of carbonate fractured-caved reservoirs.