A compound spray gun comprises a tube body having an approximate L shape; one end of the tube body being installed with a spray head; a front surface of the spray head having a plurality of water outlets which have different forms; an interior of the tube body having two flow channels which penetrate through the tube body; a receiving body filled with additive being detachably installed to a lower end of the tube body; a guide post being axially installed in the receiving body; one end of the guide post exposing from the tube body for being connected to a cleaning running water; another end of the guide post in the receiving body being connected to one flow channel; and a key being pivoted to the tube body.