The invention relates to a method for processing a large arc surface. The method comprises the steps that a bottom plate is fixedly mounted on a workbench of a machine tool; an oscillating plate is placed above the bottom plate; the bottom plate is connected with the oscillating plate by a rotating shaft; one end of a connecting shaft is fixedly connected with a side face of the oscillating plate and the other end thereof serves as a supporting point of a tooling and is fixed; a workpiece to be processed is clamped on the oscillating plate to allow the distance from the to-be-processed side face of the workpiece to the supporting point to be equal to the radius of the workpiece to be processed; after the machine tool begins operating, the workbench makes reciprocating motion; the oscillating plate drives the workpiece to swing relative to the bottom plate around the rotating shaft and make arc motion around the supporting point; and a planer tool on the machine tool planes the arc surface on the to-be-processed side face of the workpiece.