A wheel lightweight machining fixture, comprising a rotating chuck for clamping a wheel, on which radial positioning blocks for radial positioning of first stage turning of a wheel, axial positioning blocks for axial positioning of first stage turning, and corner cylinder pressure claws for pressing the wheel are uniformly distributed, a vertical lathe I turret, on which an inner rim turning tool for turning the inner rim of the wheel, an outer rim turning tool for turning the outer rim of the wheel and a clamping base are mounted, and a vertical lathe II turret, on which a central hole flange turning tool for turning the central hole and flange surface of the wheel and a spoke back cavity turning tool for turning the spoke back cavity are mounted, characterized in that two grooves are bilaterally distributed in the rotating chuck, an electric cylinder and a guide rail are fixedly mounted in the left groove, a slide block is mounted on the guide rail, the output end of the electric cylinder is connected with the slide block, a linear motor I is fixedly mounted on the slide block, an ultrasonic thickness measuring sensor I is mounted at the output end of the linear motor I, and a piezoelectric sensor I is integrated inside the ultrasonic thickness measuring sensor I; wherein when the electric cylinder drives the slide block to move along the guide rail, the position where the ultrasonic thickness measuring sensor I is in contact with a wheel spoke can be adjusted, so that the spoke thicknesses at different positions can be detected, wherein the clamping base is mounted on the vertical lathe I turret, the linear motor II is mounted on the clamping base, an ultrasonic thickness measuring sensor II is mounted at the output end of the linear motor II, and a piezoelectric sensor II is integrated inside the ultrasonic thickness measuring sensor II; through motion of the turrets, the ultrasonic thickness measuring sensor II can contact the outer rim of the wheel and detect the rim wall thickness. a rotating chuck for clamping a wheel, on which radial positioning blocks for radial positioning of first stage turning of a wheel, axial positioning blocks for axial positioning of first stage turning, and corner cylinder pressure claws for pressing the wheel are uniformly distributed, a vertical lathe I turret, on which an inner rim turning tool for turning the inner rim of the wheel, an outer rim turning tool for turning the outer rim of the wheel and a clamping base are mounted, and a vertical lathe II turret, on which a central hole flange turning tool for turning the central hole and flange surface of the wheel and a spoke back cavity turning tool for turning the spoke back cavity are mounted, characterized in that two grooves are bilaterally distributed in the rotating chuck, an electric cylinder and a guide rail are fixedly mounted in the left groove, a slide block is mounted on the guide rail, the output end of the electric cylinder is connected with the slide block, a linear motor I is fixedly mounted on the slide block, an ultrasonic thickness measuring sensor I is mounted at the output end of the linear motor I, and a piezoelectric sensor I is integrated inside the ultrasonic thickness measuring sensor I; wherein when the electric cylinder drives the slide block to move along the guide rail, the position where the ultrasonic thickness measuring sensor I is in contact with a wheel spoke can be adjusted, so that the spoke thicknesses at different positions can be detected, wherein the clamping base is mounted on the vertical lathe I turret, the linear motor II is mounted on the clamping base, an ultrasonic thickness measuring sensor II is mounted at the output end of the linear motor II, and a piezoelectric sensor II is integrated inside the ultrasonic thickness measuring sensor II; through motion of the turrets, the ultrasonic thickness measuring sensor II can contact the outer rim of the wheel and detect the rim wall thickness.