Abstract: With the gradual development of mining to the deep, rock burst disasters frequently occurred, especially the impact disaster caused by the overall fall of the hard roof of the gob in large space, which seriously affects the safe and efficient development of the mine. Based on the research background of the impact disaster caused by the surrounding rock falling above the +850 m level of the ore body of Dongshengmiao No.11 Copper Mine, the impact mechanics model was established by applying the engineering analogy method. The pillar was simplified as a beam structure. Based on the material mechanics theory and stress diffusion theory, the relationship between the maximum tensile stress, shear stress, deflection and the thickness of the cushion within the impacted ore body was established. The variation law of the three mechanical responses with the thickness of the cushion and the optimal setting thickness of the cushion were further studied. Finally, the validity of theoretical analysis of optimum cushion thickness was verified by FLAC3D numerical simulation.The research results show that: ① the maximum impact force of falling rock impacting the cushion and the displacement in the cushion respectively decreases and increases with the increasing of cushion thickness, and their reducing and increasing extent decrease with the increasing of cushion thickness; ② the maximum tensile stress, maximum shear stress, maximum deflection and their reduction extent decrease with the increase of thickness of the cushion in the pillar.③ the thickness of cushion is analyzed from the perspective of economy, safety and efficiency, and it is considered that it is most reasonable to set the cushion layer with a thickness of about 18 m. The research results can provide theoretical guidance and experience reference for the treatment of mine gob and the protection of mountain road shed.