The invention discloses an automatic machining and discharging device for valve middle joints. The automatic machining and discharging device for the valve middle joints comprises a cross plate, wherein two vertical plates are symmetrically welded to two sides of the lower surface of the cross plate; a bottom plate is welded between the two vertical plates; a through hole is formed in the center of the cross plate; a first forward and reverse rotation motor is arranged on one side of the upper surface of the cross plate; an inserting block is fixedly mounted at an output shaft of the first forward and reverse rotation motor; a threaded block is mounted at the other end of the inserting block in an inserted manner; a supporting table is welded to the other side of the upper surface of the cross plate; a cylinder is fixedly mounted on the upper surface of the supporting table; and a knife holder is arranged at the output end of the cylinder. By addition of a smearing plate, a protectingagent can smear the surfaces of the valve middle joints, the corrosion resistance of the valve middle joints is improved, the service lives of the valve middle joints are prolonged, by cooperation ofthe first forward and reverse rotation motor, a second forward and reverse rotation motor and a cylinder, automation of milling operation and discharging operation is realized, and working efficiencyis improved.