The invention relates to a device for the work of a super-high-voltage power transmission line and particularly relates to a broken strand repairing and wire smoothening device of an under-actuated super-high-voltage power transmission line of high-altitude hot-line work. The broken strand repairing and wire smoothening device comprises a clamping wire metamorphic mechanism which is symmetrical left to right, a locking mechanism and a detaching mechanism. The clamping wire metamorphic mechanism is composed of a motor, a fixing frame, a transmission screw rod, a left-right nut, a left-right first connecting rod, a left-right second connecting rod, a left-right clamping body, a subdividing nut and the like a limiting spring and a special structure are arranged at hinged parts of the second connecting rod and extending ends of the bottom ends of clamping bodies, and a tapered gear stretches out and left and right parts of the subdividing nut are respectively carried by the left and right clamping bodies. The locking mechanism is arranged on the left clamping body and a connecting pin is inserted on a left slide block in an interference fit manner and the locking mechanism has such a difference from the detaching mechanism that a fixing pin and a right slide block are integrally formed. The clamping wire metamorphic mechanism, the locking mechanism and the detaching mechanism transmit power through engaging with the tapered gear. The broken strand repairing and wire smoothening device has the advantages of less driving, more movements, simple control system and small abrasion of the subdividing nut, and has higher reliability and practical applicability.