Abstract: To study the effect of paste filling on the failure law of seam floor, taking 2153 working face of Daizhuang Mine as the engineering background, three methods, Midas/GTS-FLAC^3D coupling simulation technology, mechanics analysis of sliding surface theory and borehole water injection method, were used to obtain the failure depth of coal seam floor. The results show that the numerical simulated value of failure depth is about 3 m. The failure mode of floor is mainly tensile fracture of tensile-shear damage and the maximum vertical stress is 0.5 times as big as the initial stress. Further, the corresponding value by sliding surface theory is between 2.5 m and 3.0 m, which is in agreement with the measured value by water injection method. The failure depth of floor by paste filling is 0.2 times as deep as the caving method.