The invention provides a numerical control machining clamping and positioning device for a large thin-wall conical shell part and belongs to the technical field of numerical control machining. The numerical control machining clamping and positioning device aims at solving the problems that when machining is conducted without an external clamping and fixing tool, the final size is difficult to guarantee, the part scrapping phenomenon is likely to happen, and the amount of feed is usually reduced in order to avoid the situation, so that machining efficiency is low, time is wasted, and the period is long. A conical barrel is supported on a workbench through supporting bolts of the clamping and positioning device, and the large-diameter end of the conical barrel is placed upwards; the machined workpiece is placed in the conical barrel, and the machined workpiece and the conical barrel are coaxially arranged; and a large-end conical ring liner plate is pressed on a large-end conical stop opening of the machined workpiece, and the machined workpiece is axially fixed through pressing plate bolts and pressing plates. It is guaranteed that the machined thin-wall conical shell part is not deformed in the machining process; angular reference alignment is convenient, and axial positioning is accurate; the structure is simple, and clamping and fixing are reliable; and the manufacturing period is short, and cost is low.