During the erection of multi-bundle conductors of transmission lines, spacers shall be installed between conductors to ensure that the equivalent radius between conductors meets the requirements of relevant standards. During the existing construction process, the installation position of the spacer is marked manually. When marking, only the installation position of the spacer for a single conductor is marked, and the installation posture of the spacer cannot be guaranteed. In this paper, the four-bundle conductor is taken as an example to study the above problems. The studied marking mechanism can ensure that each sub-conductor on the four-bundle conductor has a mark, and the installation position of the spacer is more accurate. The research on the marking mechanism is mainly aimed at its structural stability, installation convenience, marking effect and identifiability, which effectively solves the on-site construction problems.