The invention discloses a power transmission line pay-off and backout spanning coaster, which belongs to the field of installing, maintenance and repair equipment for an overhead line or a cable. The power transmission line pay-off and backout spanning coaster is used for solving the problem of low work efficiency since a power transmission line needs to descend to the ground in the power transmission line pay-off and backout process under the 10kv line spanning condition. The power transmission line pay-off and backout spanning coaster comprises a carrying frame and two bilaterally symmetrical support frames, wherein each support frame comprises two support frame legs; the tops of the support frame legs of each support frame are connected; the two support frame legs form a triangular structure with the ground; the bottom ends of the support frame legs are provided with pulleys and fixing ropes; the carrying frame comprises a rotating rod and fixing rods; the rotating rod is positioned between two support rods; the two ends of the rotating rod are fixed with the pulleys; and the fixing rods are fixedly connected with the support frames. The power transmission line pay-off and backout spanning coaster has the advantages that the use range is wide; the pay-off and backout work efficiency can be obviously improved; and meanwhile, a spanned line can be protected.