The invention provides a medium-thickness steel plate air purging device. The medium-thickness steel plate air purging device is installed on a controlled cooling device and comprises a compressed air branch pipe, an air filter, an air reducing valve, a pneumatic cut-off ball valve and a jet header, wherein the jet header is connected with the pneumatic cut-off ball valve, the pneumatic cut-off ball valve is connected with the air reducing valve, the air reducing valve is connected with the air filter, the air filter is connected with the compressed air branch pipe, the jet header comprises two steel pipes and a right-angle connector, one steel pipe is welded to one end of the right-angle connector, the other steel pipe is welded to the other end of the right-angle connector, a plurality of fixing connectors are sequentially arranged on each steel pipe, a ball connector is connected to at least one fixing connector, a jet nozzle is installed on the ball connector, and the jet angle of the jet nozzle can be adjusted by the ball connector. Compressed air in a workshop enters the jet header through the compressed air branch pipe and then is jet to the surface of a medium-thickness steel plate through the jet nozzle, and therefore water and oxidized scale on the surface of the medium-thickness steel plate are removed, and the quality of the medium-thickness steel plate is improved.