Disclosed are a wheel lightweight machining fixture and method. The fixture comprises a rotating chuck, an electric cylinder, a guide rail, a slide block, a first linear motor, radial positioning blocks and the like. When the electric cylinder drives the slide block to move along the guide rail, the position where an first ultrasonic thickness measuring sensor is in contact with a wheel spoke can be adjusted, so that the spoke thicknesses at different positions can be detected. Through motion of the turrets, an second ultrasonic thickness measuring sensor can contact the outer rim of the wheel and detect the rim wall thickness. By integrating a measurement feedback system into the manufacturing process, the disclosure provides a fixture and a method for minimum entity machining of the rim wall thickness and the spoke thickness of a wheel during the first stage turning process, thereby realizing lightweight manufacturing of the wheel.