Abstract: The water inrush coefficient formula was consisted with the water pressure and the water insulation layer thickness M.In order to make the water inrush coefficient method applied to more accurately and efficiently evaluate the mine floor water inrush, in consideration of the mechanics strength and water resistance perfo rmances of each type rock, from the rock combination mode of the floor water insulation layer and the development condition of the mine pressure failure zone, the wat er inrush coefficient formula could be modified to a quality ratio coefficient formula and a strength ratio cofficient formula.The modified formulas were applied to the mi ne.The results showed that the evaluation figures drawn with the two modified formulas would not only accurately display the mine floor water inrush danger area, but C ould provide the maximum value and minimum value of the mine floor water inrush coefficients.