In order to learn of the mechanical responses characteristics of arched protection shed of bridge under rockfall impaction, the action effects of structure are analyzed by dynamic finite element method. The results show that: 1) The parts of the superstructure such as crown top, inner side of arch springing and outside of sidewall feet and the substructure′s pile foundation top and foot joint bear large load both before and after rockfall impaction; and the load on outside piles are larger than that inside piles. 2) The magnification rate of the load effect along vertical direction is larger than that 45° along vertical direction; and that 45° along lateral direction is the smallest. 3) The maximum strain rate of the structure caused by rockfall impaction is less than 1×10-3 s-1, which is within the range of quasistatics scope; the maximum rockfall penetration depth into buffer layer is 0.9 m, while the design buffer layer is 2 m in depth; the maximum and minimum strain of the structure are within the limit scope of material, which shows that the structure can bear the rockfall impaction. 4) The impaction load acting on the structure top mainly concentrates on the central part of the crown top whose area takes 16.7% of the whole top while bearing 44.9% of the impact load.