Sand cushions are commonly used in engineering to buffer the rockfall impact of the shed structure. however, the sand has a large self-weight, which increased the internal forces of the structure under static load. Due to low density and good cushioning performance of EPS foam, a composite cushion was formed by replacing some sand soil with EPS material in the sand cushion. Thus, the goal to reduce impact force of rockfall to shed gallery was achieved. Based on prototype experiments, a numerical model was established to simulate steel shed impacted by rockfall. The results of tests and simulation were in good agreement under different rockfall height, indicting the numerical model is reliable. Then the cushioning effect of composite cushion was studied. The results show that the cushioning performance of composite cushion is better than that of sand cushion when the total cushion thickness is constant. Increased with the thickness of EPS material, the shed structure bears smaller impact force, and the stress, the deflection of beams are reduced. However, the maximum compression and compressive stress of EPS material are higher with thicker EPS cushion, which is adverse for EPS material to bear impact force later. Therefore, on the basis of ensuring the safety of the steel shed gallery, it is necessary to consider the economy of EPS material and select the suitable EPS thickness.