通过选取三镜消像散(Three－mirror anastigmat，TMA)的结构形式介绍了共轴系统离轴使用的方法。TMA系统由三个二次曲面镜、一个变形镜和一个快速稳像镜构成。根据三镜系统的初级像差理论推导出了系统的初始结构，利用自动光学设计软件Zemax对初始结构进行了像差优化设计。采用两种优化方法来保证系统的出瞳与变形镜重合，以便于校正主镜的剩余误差。所设计出的光学系统的成像质量可接近衍射极限，满足了系统对成像质量的要求。

A configuration called three-mirror anastigmat (TMA) system,which is coaxial system used in off-axis situation,is discussed. TMA is made up of three conic mirrors,a deform mirror and a fast steering mirror. The initial configuration is obtained according to the theory of the first order aberrations,and then optimizes with the software of automation optical design Zemax. The exit pupil can be located at the deform mirror to correct the residual aberrations caused by the primary mirror.Two methods are applied to meet this requirement. The image quality of the optical system designed is near the diffraction-limited,and can satisfy the requirement of the usage.