A combined powder cleaning gun for an automatic powder cleaning system for mixed-line hub bolt holes, comprising a combined gun body and a gun barrel, wherein the combined gun body includes front and rear combined units (3, 5), the lateral surface of each combined unit (3, 5) includes a front splicing section (302, 502) and a rear powder absorbing section (305, 505), the diameter of the powder absorbing section (305, 505) is greater than that of the splicing section (302, 502), a powder absorbing through hole (307, 507) is formed in the center of each combined unit (3, 5), and the powder absorbing section (305, 505) of each combined unit (3, 5) is provided with a powder absorbing hole (304, 504); the diameters of the splicing section and the powder absorbing section of the rear combined unit are respectively greater than those of the splicing section and the powder absorbing section of the front combined unit, and a connecting device is arranged at each of the front and rear ends of each combined unit (3, 5); the gun barrel comprises a central gun barrel and a ball socket and platform gun barrel, the tail of the central gun barrel is connected with the splicing section of the front combined unit, the tail of the ball socket and platform gun barrel is connected with the splicing section of the rear combined unit, the head of the central gun barrel protrudes out of the head of the ball socket and platform gun barrel, characterized in that dense micro holes are formed in the side wall of the head of the central gun barrel, and two small plugs are provided to plug the powder absorbing hole of the rear combined unit, and in that the connecting devices of each combined unit (3, 5) refer to an internal threaded hole (301, 501) formed in the front end of the powder absorbing through hole (307, 507) of each combined unit (3, 5) and an external threaded section (306, 506) formed at the tail end of each combined unit (3, 5), the internal threaded hole (301, 501) and the external threaded section (306, 506) of each combined unit (3, 5) adopt mutually matched sizes, and the sizes of the internal threaded hole (301, 501) and the external threaded section (306, 506) of the each combined unit (3, 5) are completely same, wherein a sealing section (303, 503) is formed adjacent to the internal threaded hole (301, 501) of the combined unit (3, 5), and a sealing ring is installed between the rear end face of the external threaded section of the front combined unit and the sealing section of the rear combined unit. characterized in that dense micro holes are formed in the side wall of the head of the central gun barrel, and two small plugs are provided to plug the powder absorbing hole of the rear combined unit, and in that the connecting devices of each combined unit (3, 5) refer to an internal threaded hole (301, 501) formed in the front end of the powder absorbing through hole (307, 507) of each combined unit (3, 5) and an external threaded section (306, 506) formed at the tail end of each combined unit (3, 5), the internal threaded hole (301, 501) and the external threaded section (306, 506) of each combined unit (3, 5) adopt mutually matched sizes, and the sizes of the internal threaded hole (301, 501) and the external threaded section (306, 506) of the each combined unit (3, 5) are completely same, wherein a sealing section (303, 503) is formed adjacent to the internal threaded hole (301, 501) of the combined unit (3, 5), and a sealing ring is installed between the rear end face of the external threaded section of the front combined unit and the sealing section of the rear combined unit.