The invention discloses a wire tightening tool for a power transmission line lead and a wire tightening method. One end of a hand-operated screw rod is connected to a connector of a pulling plate; the other end of the hand-operated screw rod is connected to one end of a guide rod (3); the other end of the guide rod (3) is connected to a piston rod of an oil cylinder (2); the cylinder body of the oil cylinder (2) is connected to a connector of a clamping tool (1); the connector of the pulling plate is connected to the pulling plate; the clamping tool connector is connected to the clamping tool; and, firstly, the hand-operated screw rod is utilized to realize the front load transferring of long distance and small pulling force, and secondly, the oil cylinder is utilized to realize the rear load transferring of the short distance and big pulling force. The invention discloses a wire tightening device for the power transmission line, which is applicable to the replacement operation of glass insulators or ceramic insulator, short in the effective stroke, light in weight, easy in operation and high in operation efficiency.