Abstract: In the calculation of the floor failure depth, the existing mining damage is rarely considered. In this paper, by taking the mining of Group A coal seams in a certain mine as the background, the floor damage variable based on the numerical simulation and theoretical calculation was proposed, and then the method for determining the floor failure depth was put forward. Holes were drilled at the specific location of the working face roadway, the validity of this method was then verified with the parallel electric method.The results showed that the floor stress reached the peak of 19.70 MPa near the fault and the equivalent damage variable of the floor rock was D′=0.79; the maximum floor failure depth that was calculated according to the damage variable was 20.27 m, compared with the underground measured results, its accuracy reached 93.32%.The research results provided a new idea for rapidly and accurately determining the mining-induced floor failure depth.