The invention discloses a sudden-expansion and sudden-fall radial gate rear side wall aeration structure, and belongs to the field of water conservancy and hydropower. The structure comprises a radial gate, side walls, a bottom plate, a ventilation shaft, a sudden-expansion and sudden-fall water stop mechanism and side wall aeration mechanisms, wherein the side walls are located on the two sides of the bottom plate, a water flow channel is formed between the side walls and the bottom plate, the radial gate is installed on the water flow channel, the ventilation shaft is located on the downstream of the radial gate and communicates with a cavity area on the top of downstream flood discharge water flow, the sudden-expansion and sudden-fall water stopping mechanism is located on the upstream of the radial gate, and the side wall aeration mechanisms are located on the two side walls of the downstream of the ventilation shaft. According to the side wall aeration structure, under the condition that the width of an original flood discharge tunnel is not expanded, the multiple stages of side walls which are shrunk inwards firstly and then expanded laterally are arranged on the two side walls of the downstream of the ventilation shaft, water flow passes through the multiple stages of side walls after impacting the side walls through the gate, the water flow is fully aerated, the water flow on the side walls does not have a clear water area any more, and the side walls are not subjected to cavitation damage any more.