This paper introduces the design and application of a special anchoring device, which can move on a circular track, in the cable network erection project of the main supporting structure of the active reflector of the radio telescope FAST at Guizhou Observatory. The mobile trolley is the anchoring device of the cable network erection works on the ring beam. It is used to anchor the construction cableway (hanging cableway and basket cableway) and the tension end reaction frame of the steel strand pulling the radial cable, while the other end of them is anchored on the tower and the catway V-shaped platform in the center of the ring beam. The mobile platform car is effectively fixed on the ring beam with a fixed device, and the flat truss structure is small in size and light in weight, which is conducive to the effective transfer of its own cable force to the ring beam, and greatly improve its own stress condition. The platform is equipped with a slope track to allow the cable car to pass through it, ensuring the safety of cross-dimensional operation.