The utility model discloses a fixed-length small-span ground wire length measuring device, comprising a rack, a first paying-off tackle and a second paying-off tackle which are sequentially arranged between a tension machine and a tower and used for placing a ground wire, wherein the rack near the tension machine is provided with a ground wire spraying device, a laser meter counting instrument, a temperature measuring device and a ground wire tension measuring device; the second paying-off tackle near the tower is provided with a photoelectric detection device, and the ground wire spraying device, the laser meter counting device, the temperature measuring device, the ground wire tension measuring device and the photoelectric detection device are all connected with a industrial personal computer. The device disclosed by the utility model divides the length of the ground wire required to be measured into a plurality of small spans with a fixed length and mantissas and carries out measurement, greatly improves the measurement precision through using the ground wire spraying device and the photoelectric detection device in a matched mode, avoids impacts of structural extension and plastic extension of the ground wire, and improves the working efficiency and the quality; and meanwhile, the amount of the ground wire can be save by 0.2%, and the sag observation time is reduced.