Abstract: According to the deformation and motion requirement of the active main reflector of the telescope. In this paper,
a dynamic shape finding technology of cable segment is studied, and considering the deadweight and change of temperature, the
geometric model of the cable segment is built. A new method for approximating the catenary to the parabola is proposed.
According to the new method, the best reference points of the catenary segment are found.

Key words: dynamic shape finding, cable, catenary segment