Abstract: In recent years, with the fast development of astronomical science and higher requirements for astronomical telescope's performance, the ground-based extremely large astronomical optical telescopes with aperture 20 m~40 m in diameter are being actively studied and constructed internationally. With the increase of the telescope aperture, these telescopes should face even greater challenges. In order to make them meet their optical design requirements, new solutions are needed to provide adequate load sharing. In this paper, several design methods of the main structures and key components of the extremely large telescopes are summarized, the advantages and disadvantages of various schemes are analyzed, a lightweight sheet metal welding structure for the 30 m Chinese Future Giant Telescope (CFGT) is put forward, and the finite element model design and analysis are carried out. The results show that when the telescope points to the zenith, the first modal frequency is 2.3 Hz and the maximum deformation of the structure is 3.8 mm. While the telescope points in the horizontal direction, the first modal frequency is reduced to 2.1 Hz and the maximum deformation of the structure is 2.9 mm, which meets the technical requirements of CFGT. The design provides a technical reference for the development of extremely large telescopes in China in the future.