The invention discloses a vaulted thin-wall part machining method and belongs to the technical field of turning machining. The vaulted thin-wall part machining method comprises the following steps that a vaulted thin-wall part blank is manufactured; a flange of the vaulted thin-wall part blank is mounted on a locating piece; an outer wall of a side wall is supported through a first supporting piece; the locating piece is connected with the first supporting piece into a whole for locating and fastening the vaulted thin-wall part blank; the outer wall of the side wall located and fastened by thelocating piece and a second supporting piece; the outer wall of the side wall is supported through the first supporting piece so as to be further located and fastened; and the inner wall of the sidewall is located and fastened through the locating piece and the first supporting piece again, and by taking the circumference surface of the locating piece as a locating reference, the flange is machined. The vaulted thin-wall part machining method clamp a part during part machining, the machining deformation is little, the precision is high and the product quality is improved.