Abstract: Taking a ShanXi mine as the engineering background , mathematical expressions about dynamic response of cracked roof at pre-stable state is obtained through vibrating mechanics analysis. Several factors—basic top collapse step, thickness of coal seam, damping coefficient of hydraulic support and rocking elasticity of waste rock—are discussed in order to knew the influence of them on dynamic response of cracked roof. The results show that the vibration time of roof initial collapse is longer 0.25s than that of roof cycle collapse, and the vibration energy consumes 85% in 0.5s; maximum vibration displacement of roof will increase 10mm with collapse step increasing 10m, and reduce 7mm with coefficient of hydraulic support increasing one unit; dynamic response of cracked roof will be significantly lower when coal seam thickness of mining is less than 4m, and elastic modulus of waste rock is greater than 3.5GPa.