The invention relates to a lead backup protection device for live replacement of a tension insulator string, and a mounting method thereof. The device comprises a wing wire clamp, an insulating pull rope, a first operating lever and a second operating lever, wherein a connecting hook is arranged on a wire clamping slot mounting substrate of the wing wire clamp, and the left and right sides of the lower side of the wire clamping slot mounting substrate are respectively hinged with a first pull arm; the first pull arms at the two sides are respectively hinged with a wire clamping block to form a wire clamping slot, and the front ends of the first pull arms are hinged with second pull arms; the front ends of the two second pull arms are hinged and are simultaneously hinged with a U-shaped ring, and an automatic locking spring and a width limiting device are connected between the two second pull arms so that the opening width of the spring is fixed; the two ends of the insulating pull rope are respectively connected with a pole tower and the U-shaped ring, and the first operating lever is connected with the connecting hook; the second operating lever is connected with the width limiting device, and the width limiting device is opened after a lead is clamped into the wire clamping slot; the automatic locking spring retracts and drives the wire clamping block to clamp the lead. The device and the mounting method thereof have the advantages that the safety and reliability of live working are improved, and mounting and implementation are easy.