Abstract: The carboniferous-Permian No. 6 coal seam in the eastern Jungar Coalfield of Ordos Basin is an extra-thick coal seam, and the coal floor is particularly threatened by the Ordovician limestone aquifer. The mining effect will lead to the formation of the bottom mining damage zone, and new water-conducting channels may be formed, which in turn will cause sudden water disasters. Aiming at the testing problem of floor mining failure zone, the method of transient electromagnetic method in hole with moving source and receiving is proposed to obtain resistivity characteristic data of strata from floor drilling before and after mining. Firstly, the resistivity difference of the TEM method in the complete and two-layer rock model is compared by numerical simulation, and the proposed method has a good resolution for the two-layer rock model. We conducted a test at the fully mechanized top coal caving face 6119 extra-thick coal seam in Jungar coalfield, and obtained the bottom damage depth by probing the bottom electrical difference layer, and the results were verified to be accurate and reliable. The research shows that the more accurate floor failure depth can be obtained by comparing the results of pre-mining and post-mining, which provides a new method for testing the failure depth of working face under similar conditions.