The invention discloses a large-sized thin-walled cylinder part bulging tool. The large-sized thin-walled cylinder part bulging tool comprises a base, a regularly-octagonal pyramid sleeve, eight bulging sections and a nut with a flange at the lower end. A fixed column with a thread at the upper end is vertically and fixedly arranged at the center of the base. The nut and the regularly-octagonal pyramid sleeve are embedded into the fixed column in sequence from top to bottom. A gland is fixedly connected with the regularly-octagonal pyramid sleeve. A rolling guide rail is arranged on each outercone face of the regularly-octagonal pyramid sleeve. Each bulging section is divided into a horizontal segment and a vertical segment. The horizontal segments are movably connected to the base. Sliding grooves matched with the rolling guide rails are formed the inner surfaces of the vertical segments. Sliding blocks are mounted in the sliding grooves. The invention further discloses a clamping method for the large-sized thin-walled cylinder part bulging tool. The clamping method comprises the following specific steps of mounting the tool, adjusting the regularly-octagonal pyramid sleeve to belocated on the upper portion, clamping a cylinder part, performing adjusting and measuring, performing outer circle machining and detaching the part. This large-sized thin-walled cylinder part bulging tool can efficiently and reliably clamp the large-sized thin-walled cylinder part and is high in clamping accuracy.