Open type tooth mark-free power tong back-up tong

The utility model relates to an open type tooth-mark-free power tong back-up tong which comprises a back-up tong body, a single-rod hydraulic cylinder, a clamping arm, a rotating shaft, a plug pin, a front jaw plate assembly, a torsion spring, a clamping arm automatic reset mechanism, a rear jaw plate assembly and a limiting block, and the single-rod hydraulic cylinder, the clamping arm, the rotating shaft and the plug pin form a set of lever clamping mechanism driven by the hydraulic cylinder. The two groups of lever clamping mechanisms driven by the hydraulic cylinder are arranged in an inner cavity of the back-up wrench main body and are symmetrically arranged along an axis A-A symmetrical to an opening of the back-up wrench main body; and the single-rod hydraulic cylinder is fastened with the back-up wrench main body. The lever clamping mechanism driven by the hydraulic cylinder is adopted for clamping, the clamping force is large, the structure is compact, clamping is reliable, meanwhile, the tooth plate