Abstract: The present study is aimed at the calculating method for the impact forces in multiple-impact flexible systems. So a method named transient wave response approach is presented to compute the multiple impact forces by use of the transient wave propagation theory. The approach can avoid solving the impact forces from the strongly nonlinear equation coupled with impact motions. The flexible system of two flexible rods with longitudinal impacts is investigated. The numerical results show that the approach can calculate the multiple-impact forces accurately. In addition, the effects of the initial impact velocity and the length ratio on multiple-impact forces are discussed, and the phenomena of “sub-impact” are observed.