Conventionally designed with quasi-static algorithm, buffer springs of impact mechanism eventually have a short fatigue life. By building a rigid-flexible hybrid model of GCD-1500 cable drill, the main fatigue causes of buffer springs are investigated so as to optimize the design of springs attached to impact mechanism. Dynamic simulation is used to export load spectrum of dynamic responses of springs in conditions of “idle impact” and different bore depths. Nominal stress method is employed in nSoft Software to analyze the fatigue of springs. Some crucial conclusions are drawn: the fatigue damage brought by load spectrum of dynamic response is more severe than that brought by quasi-static mono-pulse circulation; as the bore depth is prolonged, the damage of one impact will increase; the damage of “idle impact” is 25 times as serious as that of one impact when bore depth is 70m.