Chinese Giant Solar Telescope is the next generation ground based solar telescope of china. Due to the characteristics of ring aperture in polarization detection and thermal control, the current design of CGST is an 8 meter ring solar telescope. The simulation of science cases and the current observations from 1m class solar telescopes indicated the necessity of such a big aperture especially in infrared bands. The integrated simulation of optical system and imaging ability such as optical design, MCAO, active maintenance of primary mirror were carried out in this paper. The results of simulation and analysis showed that the current design could meet the demand of most science cases not only in infrared band but also in near infrared band and visible band.