Overview: In order to achieve the desired performance a compact and lightweight isogrid fully integrated into the Altitude Structure is proposed. This structure is adapted to the mirror interfaces of the 30 m Chinese Future Giant Telescope. The aim of the M1 Support Structure is to provide stiff support for the Primary Mirror and, at the same time, contribute to the stiffness of the Altitude Structure, using a lightweight solution so that the unbalance of the altitude structure does not increase in an important way. Besides, the M1 Cell needs to offer an adequate interface to the different mirrors and thus avoid the generation of important local displacements at their support due to the weight of that mirrors. Furthermore, the M1 Cell must allow easy access for maintenance. The isogrid consists of a series of top and bottom plates welded to each other using a series of ribs extending in different directions and using a triangular pattern, resulting in a structure behaving like a lightweight isotropic material. The isogrid will have a constant thickness of 3200 mm to be accessed and will follow the same curved surface as the mirrors. Apart from being a lightweight solution, the fabrication and assembly of such an isogrid are simpler than those of a conventional space frame, which is the traditional solution for M1 Support Structures. Besides, the isogrid allows more open room below the mirrors, so that access from below to the mirrors for maintenance can be achieved easily and even carts up to 1 m height would be able to drive below the mirrors, which is difficult to achieve in the case of a space frame. This can be achieved using a continuous floor on the bottom plate. In order to avoid the fact that the ribs are an obstacle to the continuous floor, we propose using a modular and puzzle-like grating made of galvanized steel that can be mounted easily and the top surface is at the same height as the ribs. A grating based on 40 mm × 4 mm steel members with a spacing of 50 mm ×50 mm is proposed to fulfil the requirements. The different elements of the grating will be planar elements. Due to the low curvature of the surface containing the mirrors, it is expected that carts will be able to travel through it.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.