The invention discloses a retaining and protecting structure of a reinforcing existing line of steel-structure self-drilling type hollow anchor rod. Protecting structures are arranged on side slopes of the two sides of a roadbed. Angle iron nets are horizontally and vertically arranged on the surfaces of side slope protecting walls from the bottoms of the side slopes and the tops of the side slopes in a crossed mode in the roadbed direction, and cushion plates are arranged on nodes of the angle iron nets. Hollow anchor rods which penetrate through the cushion plates and the nodes and go deep into the ground layers of the side slopes are vertically arranged on the protecting walls of the side slopes, and hollow cavities are formed in the hollow anchor rods. Anchoring force is generated on reinforcing bodies in the ground layers behind retaining walls and the protecting walls through self-drilling type hollow anchor rods, the anchoring force is evenly exerted on the wall faces of the reinforcing bodies by means of the cushion plates and angle iron, and a formed reinforcing system is good in integrity and high in stability.