A clamping device for a protection casing of an electronic device serves to clamp a protection casing for receiving an electronic device. The protection casing includes an upper cover for covering an upper side of the electronic device and a lower cover for covering a lower side of the electronic device; and in assembly state, the upper cover is connected to the lower cover to enclose the electronic device. The clamping device comprises an upper clamping frame and a lower clamping frame for clamping the protection casing therein. A combining structure is arranged on lateral sides of the upper clamping frame and the lower clamping frame for combining the upper clamping frame and the lower clamping frame so that the upper clamping frame and the lower clamping frame clamp the protection casing tightly and thus the protection casing retains its function for a long time.