Abstract: Six feed-support towers are the key load-bearing structures of the feed support system of FAST telescope. Their function and characteristics are introduced in the paper. The work on the structural design and optimization of 6 towers is conducted in response to all kinds of technical specifications required by the design task. Finally, simulation models of the towers are built for computational check of the first natural frequency, which is the key specification of tower design. The numerical results are also compared with the frequency measurements on site. The results show a good consistency between them.