The invention discloses a replacement tool for tension double-string insulators in an overhead transmission line and a replacement method. The double-string insulators comprise two insulator strings;two ends of the two insulator strings are respectively connected via a double connection plate; the replacement tool includes a line tightening rod, a screw rod and a plurality of support leveling clamps; the line tightening rod is connected to the screw rod; two ends of the line tightening rod and the screw rod are connected to the double connection plates; the support leveling clamps are connected to the line tightening rod; and two clamping grooves for inserting two strings of insulators in parallel are formed on each of the support leveling clamps.