The accurate measurement of conductor length is a key issue in prefabricated wire construction. However, due to the lack of accurate measurement technology of real-time spreading length of conductors, the existing prefabricated wire construction technology is too large to be popularized. Therefore, combined with the engineering application requirements of prefabricated wire construction, and taking the function of accurate measurement of conductor length and printing function as the functional goal, an accurate length measurement equipment suitable for prefabricated wire construction conditions was developed. In terms of hardware, incremental photoelectric encoder is selected to collect the length information of the wire, and long-distance radio (LoRa) technology is used for wireless data transmission, and when the unfolding length reaches the threshold, the drive circuit is designed to control the paint spray pump for painting and painting; The above functions realize the need for free charging during construction through a dedicated power supply module. In terms of software, the length measurement algorithm was designed, and a real-time wire spreading measurement system based on handheld terminal was developed. The developed length measuring equipment has been successfully applied to actual engineering, and the deviation value between the observation file sag and the design arc sag after the measured frame line is 4.57%, which meets the engineering design requirements.