Abstract: In order to study the degree of difficulty of breaking rocks and the associated controls for dynamic breaking in percussion drilling, a theoretical model based on the principal of damage due to inherent defect. This model incorporated rock dynamic fracture strength, breaking time and energy consumption. Further, the failure strength, breaking time and energy consumption characteristics in the process of rock breaking were analyzed by means of the impact test on sandstone with the split Hopkinson pressure bar (SHPB). Results indicate that calculating result with the theoretical model is basically consistent with the results from laboratory tests, tand he relationship between the strain rate and three parameters as dynamic load strength, breaking time and energy consumption of sandstone appears to be a power function. When the strain rate increases in the range from 60 s-1 to 115 s-1, the dynamic load strength is 1.33-1.83 times higher than the static load strength, and the breaking time decreases from 84 μs to 52 μs rapidly. Moreover, the greater the strain rate and energy consumption, the smaller the rock fragments. The research results in this paper can provide a reference for evaluating the degree of difficulty in dynamic rock breaking and improving the rock breaking efficiency by using impact loads.