A fixture for a thin-walled workpiece includes two clamping devices. Each of the clamping devices has a metal carrier and a damper. The metal carrier has a carrying portion and a supporting portion, where the supporting portion has a stair portion having a plane surface and a standing surface with a slope. The damper has a metal clamping portion and a damping portion. One end of the metal clamping portion is formed as an inclined surface. The damping portion has at least two elastic layers and at least one metal layer, which are laminated in an interlacing arrangement with the same slope of the inclined surface. One of the elastic layers is disposed to connect the inclined surface. The end of the metal clamping portion connecting the elastic layer is located on the stair portion, while the opposite end of the metal clamping portion protrudes out of the supporting portion.