The invention provides an overhanging type power transmission line galloping prevention device, and belongs to the field of power transmission line parts. The overhanging type power transmission linegalloping prevention device comprises a shell and an air damper which is hung in the shell, wherein the air damper is internally provided with a piston with a piston rod; the piston is provided with aplurality of flow limiting holes; the flow limiting holes are diameter-changing small holes with two large ends and narrow middle parts. The piston separates the air damper into an upper air chamberand a lower air chamber; the lower air chamber is internally provided with a compression spring; two ends of the compression spring are fixedly connected with the piston and the bottom of the shell respectively; one end of the piston rod is fixed with the piston, and the other end of the piston rod penetrates out from a perforated hole in the bottom of the air damper. When a power transmission line gallops, galloping kinetic energy is converted into elastic potential energy through the movement of the piston; an overhanging type hanging-up galloping prevention function is realized in a mannerof hanging the air damper in the shell; damping performance of the air damper is increased through the diameter-changing flow limiting holes; furthermore, the vibration absorption and buffering effects of the air damper are improved.