The invention discloses a machining method of an ultra-thin and oversized arc-shaped plate. The machining method comprises the following steps that firstly, rough machining is conducted through a planning machine; and secondly, finish machining is conducted through a numerical control milling machine. In the machining process of an arc-shaped face, in order to control bulging of a workpiece, a plurality of long strip pressing plates are parallelly pressed on the workpiece, the two ends of the long strip pressing plates are compressed through compressing plates, and fixed inside T-shaped grooves of a square box by pressing plate bolts. A plurality of puller bolts butting against the upper surface of the arc-shaped face are arranged on the long strip pressing plates. According to a numerical control program, middle arc faces of the long strip pressing plates are subjected to finish machining. After finishing, the long strip pressing plates are displaced to the finish machined surfaces to be clamped. The numerical program once more, and the unmachined arc faces are subjected to finish machining again according to the numerical program. In order to control tearing of an ultra-thin edge, a movable pressing plate is pressed on the thin edge of the workpiece in the finish machining process, and displacement is conducted once every time cutting is conducted for one time. In order to control deformation, produced by heat, of the workpiece, cold water is poured to cool the workpiece in machining. The phenomena of production of bulging and thin edge tearing of the workpiece is controlled, and the quality is increased by a large margin.