An aluminum alloy hub positioning fixture, comprising: - a compressed air system for charging air to a closed space, wherein a pressure gauge is mounted at the front end of the compressed air system, and an electromagnetic valve is mounted at the front end of the pressure gauge, characterized in that it further comprises: - a vacuum system for extracting vacuum from a closed space, wherein a vacuum gauge is mounted at the front end of the vacuum system, and an electromagnetic valve is mounted at the front end of the vacuum gauge, - a lower rotating shaft, one end of which is connected with the trapezoidal taper sleeve A via a bolt, and the other end is connected with the bearing seat via a bearing, wherein a lower cylinder can drive the rotating shaft to ascend, till the trapezoidal taper sleeve A connected with one end of the lower rotating shaft is in contact with the central hole of the hub, - a upper rotating shaft, wherein a bearing seat is mounted between the upper rotating shaft and the upper cylinder, and one end of the upper rotating shaft can rotate axially around the bearing seat, and a trapezoidal taper sleeve B is mounted at the other end of the upper rotating shaft via threaded connection, wherein a cylinder can drive the upper rotating shaft to descend, till the trapezoidal taper sleeve B is in contact with the cap section of the hub, wherein a closed space is formed among the trapezoidal taper sleeve A, the trapezoidal taper sleeve B and the hub, - a metal hose, wherein the electromagnetic valve and the electromagnetic valve are connected with one end of the metal hose, and the other end of the metal hose is connected with one end of the metal pipe in the bearing seat, wherein the vacuum system can extract vacuum from the closed space via the metal pipe and the metal hose, so that the trapezoidal taper sleeve A and the trapezoidal taper sleeve B can be in tight fit with the hub under the action of atmospheric pressure, wherein the compressed air system can charge air into the closed space via the metal pipe and the metal hose, so that the trapezoidal taper sleeve A and the trapezoidal taper sleeve B can be separated from the hub, - a servo motor, which is assembled together with the belt pulley via the belt, and drives the belt pulley and the lower rotating shaft to rotate via the belt, and the lower rotating shaft drives the hub and the upper rotating shaft to rotate together, wherein rubber sheaths are mounted on the surfaces of both the trapezoidal taper sleeve A and the trapezoidal taper sleeve B. - a compressed air system for charging air to a closed space, wherein a pressure gauge is mounted at the front end of the compressed air system, and an electromagnetic valve is mounted at the front end of the pressure gauge, - a vacuum system for extracting vacuum from a closed space, wherein a vacuum gauge is mounted at the front end of the vacuum system, and an electromagnetic valve is mounted at the front end of the vacuum gauge, - a lower rotating shaft, one end of which is connected with the trapezoidal taper sleeve A via a bolt, and the other end is connected with the bearing seat via a bearing, wherein a lower cylinder can drive the rotating shaft to ascend, till the trapezoidal taper sleeve A connected with one end of the lower rotating shaft is in contact with the central hole of the hub, - a upper rotating shaft, wherein a bearing seat is mounted between the upper rotating shaft and the upper cylinder, and one end of the upper rotating shaft can rotate axially around the bearing seat, and a trapezoidal taper sleeve B is mounted at the other end of the upper rotating shaft via threaded connection, wherein a cylinder can drive the upper rotating shaft to descend, till the trapezoidal taper sleeve B is in contact with the cap section of the hub, wherein a closed space is formed among the trapezoidal taper sleeve A, the trapezoidal taper sleeve B and the hub, - a metal hose, wherein the electromagnetic valve and the electromagnetic valve are connected with one end of the metal hose, and the other end of the metal hose is connected with one end of the metal pipe in the bearing seat, wherein the vacuum system can extract vacuum from the closed space via the metal pipe and the metal hose, so that the trapezoidal taper sleeve A and the trapezoidal taper sleeve B can be in tight fit with the hub under the action of atmospheric pressure, wherein the compressed air system can charge air into the closed space via the metal pipe and the metal hose, so that the trapezoidal taper sleeve A and the trapezoidal taper sleeve B can be separated from the hub, - a servo motor, which is assembled together with the belt pulley via the belt, and drives the belt pulley and the lower rotating shaft to rotate via the belt, and the lower rotating shaft drives the hub and the upper rotating shaft to rotate together,