Abstract: The effect of the external and internal stress field caused by the basic roof lateral fracture is expounded. The mechanical criterion of the basic roof lateral fracture is deduced on the basis of the elastic foundation beam theory. Taking the geological conditions of a mine N2103 working face as the project background, we research the bending moment changes of basic roof along the side direction, and compare with the results of field survey and borehole camera, the results show that the theoretical calculation of the maximum moment in the gob edge 5.6 m to 7.4 m of the site survey, failure zone range to the goaf edge of 5.454 to 6.847 m is consistent with the theoretical results. The research results show that the mechanical model can well judge the basic top and lateral fracture position.