Abstract: In the traditional calculation of mining failure depth, it is considered that the floor structure is intact and the actual rock mass damage is not taken into account. Taking the Panbei mine working face 11113 as the background, the integrity and damage of floor mining stress changes were analyzed by FLAC^3D. The damage variable of floor rock and the failure depth of bottom plate were deduced and calculated. In order to verify the effectiveness of the method, the calculation results were compared and analyzed with measurement results. The results show that the maximum value of the mining stress appears in the front and rear of the coal wall. When the floor is intact, it is 14.8 MPa, and it is 17.5 MPa when the floor is damaged. The damage variable of the floor rock is 0.574. Based on the damage variable, the maximum failure depth of the floor is 16.15 m. Comparing the results of parallel electrical prospecting of 16.00 m, the method is accurate in calculation. The research results can provide a new idea for determining the failure-depth of the floor mining rapidly and accurately.