The active reflector of the FAST project at the National Astronomical Observatory adopts a large cable structure, which is mainly composed of 6670 cables, 2225 nodes, and 2225 lower cables. Due to the constraints of complex terrain, the installation of the active reflective surface cable network in this project adopts a construction cableway that can continuously move with the installation of the cable network. The upper end of the construction cableway is anchored on the ring beam mobile trolley, and the lower end is anchored on the ring cable suspension leg. During the construction period, the load acting on the support legs of the circumferential cable crane by the construction cableway is relatively large, and a large number of construction personnel are working on the construction cableway. The stability of the support legs of the circumferential cable crane is crucial, while also considering minimizing the impact range of cross operations. Therefore, this article focuses on the design and calculation analysis of the lower ring cable suspension support leg of the construction cableway