Abstract: Taking the condition of fully-mechanized working face in Xinglongzhuang coal mine as background,using mutual authentication method of numerical simulation and live ultrasound imaging test,a comprehensive comparative study on the failure characteristics of coal seem floor under the mining is made.The numerical simulation indicats that the vertical stress is "saddle-shaped" distribution and the shear stress is roughly "butterfly-shaped" distribution in the workface.Field measurement studies show that the fracture development is obvious within the 16 m range under the seam floor of 10302 mechanized caving face,but the fracture development is relatively less exceed the range of 16 m.The depth of deformation failure of coal seam floor is 16 m by the comprehensive analysis,and the results provide a reference for safety mining and mine water disaster control of Xinglongzhuang coal mine under the same condition.