The invention relates to a self-centering clamp for a thin-walled part. The self-centering clamp comprises a mandrel, an expanding sleeve, an adjusting nut and a retaining ring, wherein the mandrel adopts a conical body; the inner wall of the expanding sleeve adopts a conical surface matched with the outer wall of the mandrel, and the outer wall of the expanding sleeve is a cylindrical surface; the expanding sleeve is matched and connected with the conical body of the mandrel through the conical surface of the inner wall; the front end of the expanding sleeve is connected with the step end surface at the rear end of the mandrel through a spring; the rear end of the expanding sleeve is contacted and connected with the adjusting nut through the retaining ring, and the adjusting nut is screwed at the threaded end of the mandrel; the expanding sleeve is sleeved with a flexible positioning sleeve. The self-centering clamp for the thin-walled part is simple in structure, workpieces are convenient to load and unload, self-centering can be realized, particularly, after the flexible positioning sleeve is used, the deformation of the thin-walled part is small in the machining process of clamping the thin-walled part, the machining precision is improved, and the coaxiality and the perpendicularity of the machined thin-walled part can be guaranteed; the expanding sleeve is loosened by the spring, so that the part is convenient to load, unload and machine.