The invention discloses a jumper sag measuring device which comprises a support mechanism, positioning mechanisms and a measuring mechanism, wherein a cross elbow is mounted at the upper end of the support mechanism; the positioning mechanisms are respectively mounted on two sides of the cross elbow; each of the support mechanism and the positioning mechanisms respectively comprises a support rod and a positioning rod; the support rods and the positioning rods are all composed of high-voltage insulating telescopic rods; the measuring mechanism comprises a rocker rotating wheel, a measuring line and a measuring cone; the rocker rotating wheel is mounted at the lower end of the support mechanism; one end of the measuring rope is connected with the winch of the rocker rotating wheel; the measuring cone is mounted at the other end of the measuring rope after the other end of the measuring rope penetrates through the top of the cross elbow. Compared with the prior art, the jumper sag measuring device is capable of implementing live line measurement, the measuring time can be greatly shortened, and moreover only one operator is needed to complete the measurement on a tower, so that the working intensity is greatly alleviated, and the working efficiency is high; length measurement data of a jumper sag is relatively accurate, and thus an effective and professional measuring tool can be provided for a windage yaw prevention transformation construction decision of new or old lines.