To solve the rockfall protection problems of rock-sheds along highways and railways, a piston rod point-supported flexible buffer system is proposed. Consisting of buffers, ring nets, support ropes and piston rods， the buffer system is supported on the top of a rock-shed and can provide buffer protection for the rock-shed structure. To study the mechanical behavior of the buffer system, a substructure model was designed and an impact test of 25kJ was carried out. The loading path and deformation feature, as well as the internal force response and system buffering characteristics were emphatically analyzed in combination with the test and numerical simulation. The results show that the substructure can successfully intercept a block with impact kinetic energy of 25kJ. The buffering process is characterized by three stages, i.e. relaxation deformation, compression deformation and deformation resilience. Compared with the steel column support model, the piston rod point-supported buffer system can reduce the maximum impact force by about 30%, and increase the impact time by 67%. Meanwhile, compared with those of the sand cushion layer and the EPS cushion layer, the maximum impact force of the substructure model reduces by about 69% and 61% respectively under the same impact energy. By adjusting the system configuration, the performance curve and the corresponding approximate formula are obtained under different spring stiffness conditions.