The utility model provides a clamping device for machining the outer diameter of an irregular blank through a general lathe. The fixture comprises a front clamping circular plate and a rear clamping circular plate, two surfaces of the front clamping circular plate are respectively a general lathe clamping surface and a blank clamping surface; one side of the rear clamping circular plate is a blankclamping surface; the other side is an ordinary vehicle connecting surface; a round hole used in cooperation with a center of a common lathe is formed in the center of a connecting face of the commonlathe, a sandwich clamping device for clamping a blank is arranged between a front clamping round plate and a rear clamping round plate, clamping eccentricity is eliminated, potential safety hazardscaused by infirm direct clamping of the common lathe are avoided, complexity of repeated clamping and alignment is also avoided, clamping reliability is guaranteed, and clamping time is shortened.