Abstract: Based on the field test data, the damage and fracturing of the mine floor and the pattern of fault activation during the backstopping of the working face are evaluated by the combined method of similar material tests and numerical simulations. Some conclusions are drawn that the spatial differences of the permeability of the rock stratum floor can be simulated by water pipes with different inner diameters; the water pressure can be modulated by adjusting the height of the water column in the water pipe to meet the design requirements; a higher burial depth of the coal stratum, confined water pressure and throw of the fault promote more chances for water-inrush, while a larger width of the water-resistant coal pillar at the fault helps avoid water-inrush events; and the physical tests and numerical calculations are used to simulate the complete process of the formation of cracks at the floor due to mining, fault activation and formation of water-inrush channel during backstopping, and the mechanism of formation of the water-inrush channel at the floor fault structure is revealed. The conclusions provide significant references for the design of water resistant coal pillar during backstopping of the coal stratum above the confined water with fault defects.