To ensure the safety of rock-shed structures against rock falling, it is important to study the issues of: ① establishment of evaluation method of impact force due to rock falling, ② making clear the dynamic behavior of rock-shed under impact loading and ③ development of high perfor-mance absorbing system. In this study, an evaluation method on the transmitted impact force of three-layered absorbing system is proposed. This absorbing system is develped by authors and composed of three layeres (sand top layer, RC core slad and EPS (Expanded Poly-Styrol) bottom layer). This method was derived based on ① the conservation rule of momentum among falling rock, sand layer and RC core slad, and ② the relationships between the transmitted impact energy to the bottom layer and the plastic strain energy of the bottom EPS layer. Comparing the results obtained by this method with experimental ones, it was clear that the proposed method can be practically applied to evaluate an impact force for three-layered absorbing system.