Aiming at the problem of machining the inner wall of thin shell with large arc on the common lathe, an optimum method for machining the inner wall of largearc thinwalled shell by means of lever swing clamping device was presented. The lever swing clamping device based on the principle of two power rods could be realize the uniform circular motion around the rotating shaft of the cutter bar by the pulling of the drive screw through the optimized design of the screw retract mechanism and the rotary body of the cutter body. The common lathe would be able to achieve technical requirements of machining the inner wall of thin shell with large arc by this method. The experimental results using computer aided design software Pro/E and graphic method show that the key technical parameters of the lever swing clamping device are optimized and designed reasonably, and the expected machining accuracy can be achieved. The optimized method for machining the inner wall of thin shell with large arc enlarges the using range of the common lathe in the enterprise, improves the utilization rate of common lathe, and has some application value.