Abstract: The structure of reinforced concrete (RC) slab with cushion layer composed of sandy soil is widely used in the prevention and control of high-level single rockfalls and rockfall group in mountainous areas. In order to study the impact attenuation law and the failure mode of RC slab under the rockfall load, an outdoor series impact test was carried out. The results show that an increase in the thickness of the cushion can effectively reduce the maximum impact force, and the peak acceleration increases with the thickness of the cushion, especially when the thickness of the buffer layer is 0.1 m and 0.2 m, the maximum value increases sharply. It can be obviously observed that there exists an exponential relation between the peak acceleration and the thickness of the cushion. According to the principle of dimensional analysis, the maximum impact depth of the cushion layer is directly proportional to the square of the kinetic energy, and the calculation formula is inversely proportional to the maximum incident impact force, respectively. The maximum impact depth of the cushion layer is also in good agreement with the actual measured value. The attenuation rate of the incident impact force in the cushion layer increases exponentially with the increase of the thickness of the cushion, and the peak impact force can be attenuated by about 70% under the thickness of the cushion layer of 0.6 m. With the increase of the cumulative impact energy level, the RC slab undergoes bending initiation and expansion, secondary bending cracks, shear cracks appearing, and further central bending cracks penetration, At the end of the test, the RC slab showed the typical bending failure characteristics.