在冲击凿岩机械系统中，钻头对岩石的作用力与凿深的关系曲线反映了钻头与岩石相互作用机理，而钻头波阻特性是获取这种关系曲线的前提。提出了一种基于特征线和两点应变测试法来反演计算钻头波阻方法。首先应用特征线网格，描述应用力波在变阻杆中传播规律，分别建立依空间和依时间波动分析方程；然后提出了根据弹性杆上一点状态矢量依次计算钻头波阻的反演原理，介绍了由于弹性杆两点应变求解任意一点状态矢量的方法；最后对基于特征线的杆波阻特性两点应变反演方法进行了验证和讨论。

The force-penetration relationship curver of rocks reflect interaction mechanism beteen the drill bit and rocks in the percussive drilling mechanical system,but the varable characteristics impedamce of a drill bit is essential to obtain the .A new impedance of a drill bit is essential to obtain the curves.new inverse method is proposed to estimate variable characteristics imperamce of the dill bit from the strains in a drill rod using two-point strain measurement and characteristic lines.Firstly,this paper describes stresswave propagation on a rod with variable characteristics impedance and establishes fht time and space analysis equations using a grid of chatacteristics lines.Secondly,a new inversion principle is proposed to calculate the variable characteristics impedance of drill bit in turn,according to a state vector at one point of the rod,and a method is introduced to calculate the state vector at any point suing two-point strain of the rod.Finally,the inversion meahod using two point steain of the rod and characteristic lines is validated and discussed,which can estimate variable characteristics impedance of the bit.