Abstract: A new optimized design of large aperture mirror is presented, the optimum mirror size is obtained by using Design Of Experiment, optimization module embedded in Isight which integrates with SolidWorks and ANSYS. Subjected to deformation of gravity and 60℃/-40℃ as well as first order natural frequency, design target is to minimize the mass of oval mirror, the weight is reduced to 51％. The deformed node of mirror is fitted to Zernike polynomial, imported into codeⅤ. Then the spot diagram of optical system dependent on temperature and gravity is obtained, and the deformed mirror effect on optical performance is achieved.