By taking an actual on-axis Three Mirror Anastigmatic(TMA) system with a Φ600 mm primary mirror for example,the influences of the surface irregularities of primary mirror,secondary mirror and tertiary mirror on Gaussian focus wave-front error were analyzed,and the mathematic expressions of the influences were fitted.Circle field fixed Zernike polynomial was used as an optic-mechanic interface to analyze the environment influence on primary mirror and system performance degeneration.Finally,by taking the result as reference,the supporting structure of primary mirror was improved.Based on the Marechal criterion and environment endurance,the manufacturing accuracy of primary mirror is deduced,which shows that it should be higher than λ/36.5.