For nonsmooth systems with dry friction, the transitional matrix was deduced from the cocycle at the nonsmooth instants, and then a numerical method for calculating Lyapunov exponents was introduced by means of the transitional matrix. 对带干摩擦的非光滑动力系统,在不连续点利用闭上链(cocycle)得到一个传递矩阵,由此给出一种非光滑动力系统Lyapunov指数的数值计算方法。