The invention discloses a clamp and method for machining the rim of a disc-shaped sheet part. The clamp comprises a male die, a female die and a top plate. The male die is of a round flange plate structure. One face of the male die is provided with a ringlike protruding portion. Multiple male die mounting holes are formed in the rim of the male die. A female die hole is formed in the center of thefemale die. One face of the female die is of a boss structure and provided with a ringlike groove. The radius of the ringlike groove is the same as that of the ringlike protruding portion. Multiple female die mounting holes are formed in the rim of the female die. The top plate is of a disc structure. A top plate through hole is formed in the center of the top plate. One side of the top plate isprovided with a top plate ringlike groove. By means of the clamp and method, the problem of removing excess materials on the inner circle and the outer circle of the disc-shaped sheet part can be wellsolved; turning operation can be conducted on the inner circle and the outer circle of the part under the circumstance that the internal structure of the part is not damaged; the qualification rate of products is greatly increased; and meanwhile, the clamp is simple in structure and great in universality and convenient to dismount and mount, an operator can operate the clamp easily, labor intensity is greatly lowered, and production is implemented in a safe manner without any hidden danger.