The invention relates to a clamp for finely grinding an outer circle of an eccentric cylinder. The clamp comprises an ejector pin clamp, wherein the ejector pin clamp comprises a front ejector pin connected with a main shaft turntable of a grinding machine and a rear ejector pin arranged on the grinding machine; a core rod is arranged between the front ejector pin and the rear ejector pin; an eccentric body sleeves the core rod; a first clamping plate and a second clamping plate are respectively arranged on two sides of the eccentric body and are connected through a positioning pin; a fastening screw is arranged on the outer side of the second clamping plate. The clamp has the advantages that the center is not required to be adjusted, parts are quickly clamped, and the parts are uniformly stressed.