Abstract: The statistical formula of the current failure depth of coal seam floor can't fully reflect the floor failure depth under the influence of great mining depth an d different mining heights.In order to calculate the failure depth of the coal seam floor more accurately, and guide the production safety and take waterproof measures, i t is necessary to establish the floor failure depth statistical formula.In this paper, by making situ test and analyzing references, the authors collected 21 measured data of the floor-broken depth below depth over 400 m.By regression analysis of the data, the statistical formula of floor failure depth in great buried condition were found an d then were analyzed in terms of applicability.Additionally, on the basis of the measured results, the influence of faults, large mining height and slice mining in extra-thic k coal seams were analyzed and the statistical formula were revised.Research results for the mining face above Bearing water had practical value on achieving producti on safety and formulating the water contral measures.It also has academic significance on coal mining above water body.