The invention discloses a side slope protecting device which comprises a blocking wall and a damping device, wherein the cross section of the blocking wall is in an L shape, and the damping device is arranged on the rear side of the blocking wall. In the process that the blocking wall is impacted by landslide sand and gravels and accordingly slides backwards, the damping device is used for supporting the blocking wall forwards and providing damping force. By arranging the blocking wall capable of sliding at the slope toe, when the slope surface slips, the falling sand and gravels impact on the blocking wall, so that the blocking wall slides backwards under the damping force of the damping device, the impact force of the falling sand and gravels on the blocking wall can be greatly reduced, the effect that the blocking wall is subjected to uniform and small impact force is guaranteed, damage of the blocking wall is avoided, the effect that the falling sand and gravels are effectively blocked is guaranteed, and the safety of the road surface is improved. Meanwhile, the construction area of the blocking wall is small, the damping device can be directly placed and installed after the finished damping device is manufactured, the installation period and construction period are short, the cost is low, the structure is simple, and installation is easy.