与传统折射光学系统相比，离轴反射光学系统具有小体积、轻量化和无色差等特点，因此被广泛应用于望远镜系统和空间观测系统等领域。随着目前自由曲面的广泛应用，首先分析了离轴三反光学系统的初始结构参数确定方法，然后在系统的主反射镜设计中引入 Zernike边缘矢高形式的自由曲面，最终设计了一款有效焦距为 700 mm，视场角为 10°，F/#为 4.5，系统总长为 597.58 mm的离轴三反光学系统。该系统在 71.4 lp/mm处各视场的调制传递函数（MTF）值均大于 0.28，畸变均小于 0.1%，结果表明，该系统在有效视场内成像质量较好。该系统的设计方法对类似的离轴三反光学系统设计具有一定的参考价值。

Compared with the traditional refraction optical system, the off-axis reflection optical system has thecharacteristics of small volume, light weight and no chromatic aberration, and thus it is widely used in the field oftelescope system and space observation system. With the widely use of the free surface, at first, the initial structureparameter determination method of the off-axis three-mirror reflective optical system is analyzed. And then, the freesurface with the Zernike polynomial to design the main mirror of the optical system is applied. At last, the off-axis three-mirror reflective optical system is designed, and its effective focal length is 700 mm, field of view is 10°, rela.tive aperture is F/# is 4.5, total length is 597.58 mm. The modulation transfer function (MTF) in every field angle ishigher than 0.28 at 71.4 lp/mm, and its maximum distortion is less than 0.1%, and the results show the image quali.ty of the optical imaging system is very good. Therefore, the design method of the optical system has the certain ref.erence value for similar off-axis three-mirror optical system design.