The invention provides an automatic machining device for painting rotor antirust paint. The automatic machining device for painting the rotor antirust paint comprises a single-product discharging device, a mechanical arm device, an antirust paint painting device and a finished product bin. The single-product discharging device comprises a hopper, a first open slot component, a second open slot component, an open slot air cylinder and a single-product discharging machine frame. The mechanical arm device comprises a first motor, a first ball screw pair, a first movable plate, a second movable plate, a gas claw, an up-down air cylinder and a mechanical arm device machine frame. The antirust paint painting device comprises an antirust paint painting motor, rollers, a paint loading box and an antirust paint painting device machine frame. The finished product bin is installed in the position, below the gas claw, of a discharging position of the mechanical arm device. By using the automatic machining device to paint the rotor antirust paint, the steps of manually and circularly putting on rotors to be painted and taking down finished rotors are omitted.