Abstract: The downward extension depth of surface fissures with coal mining in loess covered area directly affects the growth of vegetation and the leakage of water resources in coal mining subsidence area.Therefore, the vertical extension law of surface fissures with coal mining in loess overburden area had been studied by means of soil mechanics theory analysis, surface observation, physical similarity simulation, borehole micro-resistivity scanning imaging logging and so on.The results show that according to Moorku’s ethics, the limit depth of surface fissures with coal mining in the study area is -4.2 m, and the observed depth of surface fissures is less than it.The results of physical similarity simulation show that the vertical extension depth of surface fissures with coal mining area is -15 m, which indicates that there are hidden fissures in the loess covered area under the limit of surface fissure occurrence depth.Field measurements show that fissures are well developed in 0-6 m with coal mining in the loess overburden area, small fissures are discontinuous in -6-13 m, concealed continuous cracks are present in -13-15 m, and no fissures are found in more than -15 m, which verifies the results of physical simulation and theoretical research.The research results provide a basis for water preserved mining engineering.