The invention discloses a clamp with a cambered surface. The clamp comprises a base, a cambered pressing board provided with a cambered surface for bonding with a workpiece is movably mounted on the base, the radius of the cambered surface is smaller than that of the cambered surface of the workpiece, the other surface opposite to the cambered surface of the cambered pressing board is a plane, and a press mechanism acting on the plane is arranged on the base. During the machining, the workpiece is sleeved on the periphery of the cambered pressing board, the plane of the cambered pressing board is pressed tightly by the press mechanism, and large press force can be provided, so that the cambered surface of the cambered pressing board can be well bonded with an inner side cambered surface of the workpiece. Compared with the prior art, the clamp solves the problem of difficult clamping and locating due to the uneven blank surface when traditional large machine tool parts are machined. The cambered surface is utilized for pressing, so that the clamp can be well bonded with the machined workpiece surface, the clamping and positioning accuracy is high, and the clamping and positioning effect is good.