离轴三反系统具有无中心遮拦、成像质量好、视场大和结构紧凑等优点，因此也越来越多地被用做空间望远镜的结构形式。首先针对光学系统设计的指标要求，分析了光学系统结构形式，确定系统光学参数，设计了光谱范围0.4～0.8 μm、焦距f′=4000 mm、相对孔径1/10、视场角2ω=2.08°的离轴三反式光学系统。设计的光学系统成像质量良好，在空间频率62.5 lp/mm处，各视场的调制传递函数值大于0.5，成像质量接近衍射极限，满足系统设计要求。同时分析了主镜、次镜和三镜的失调对系统调制传递函数的影响，结果表明次镜的失调对系统的影响远大于主镜、三镜失调的影响，为系统装调工作提供参考。

Off-axis three-mirror system has the advantages of good imaging quality of vision, large field, compact structure and no central obscuration, so it is increasingly used as the structure of the space telescope. According to the requirement of optical parameters of the optical system design, an off-axis three-mirror telescope system is designed. It has a spectral region from 0.4 μm to 0.8 μm, a focal length of 4000 mm, a relative aperture of 1/10 and a angle of vision of 2.08°. For the designed optical system, the imaging quality is good, at the spatial frequency of 62.5 lp/mm, the modulation transfer function (MTF) value of each field of vision is greater than 0.5, and the imaging quality is close to the diffraction limit. The design result satisfies the requirement. Meanwhile, the effects of mismatch of the primary mirror, the secondary mirror and the tertiary mirror on the MTF of the system, and it is found that mismatch of the secondary mirror shows the greatest influence. This may provide reference for the assemble work of system.