Abstract: Based on semi-infinite body theory of elastic mechanics space, the mechanical model of floor force along the coal seam was established, the horizontal stress at any point of coal floor was calculated during the advancing process of working face. Based on stope conditions of Heze Longgu Mine 1302 working face, FLAC^3D numerical simulation software is used to conduct numerical simulation of floor failure features during the advancing process of working face. The research shows that the maximum damage depth of mining floor is about 15 m after coal seam mining. Horizontal stress of gob floor is "concave type" distribution; with advancing of working face, the horizontal stress near coal wall at both ends of goaf appears concentration effect. Adopting drilling double-ended sealing leak detection devices to do field test for floor failure depth of 1302 face, the actual measurement shows that the maximum damage depth of 1302 face floor is 14 m, which is basically consistent with numerical simulation result.