离轴三反射(TMA)系统是基于同轴三反射系统，通过视场离轴及孔径离轴实现无中心遮拦。传统解法需通过三反射镜遮拦比与放大率,来确定同轴结构的间隔等参数，该方法不利于直接限制系统筒长。在传统解法的基础上，提出一种通过给定三个反射镜间隔及三镜到像面距离，确定同轴结构的方法。利用Matlab 软件设计程序求解初始参数；利用Zemax 光学设计软件进行优化。根据是否有中间像面，分别设计得到焦距为1500 mm，入瞳250 mm 的Cook 式和Wetherell 式离轴三反射系统。结果显示，两种光学系统调制传递函数在50 lp/mm 处均大于0.6，点列斑均方根半径小于5 μm 。该方法直接有效的控制了系统长度，设计结果像质满足要求。

Off-axis three-mirror (TMA) systems are based on coaxial three mirror systems, which can avoid the obstructions through field off-axis and aperture off-axis. Traditional methods obtain coaxial system parameters such as structure intervals by calculating obscuration ratios and amplifications three mirror, which fails to limit the physical size of system directly. Based on traditional method, a new method is proposed to calculate coaxial configuration parameters by offering the interval of three mirror and distances between three mirrors and image plane. Configuration parameters are initialized by Matlab and further optimized via Zemax. According to the existence of an intermediate image or not, Cook TMA and Wetherell TMA are designed with effective focal length of 1500 mm and entrance pupil of 250 mm. Experimental results demonstrate that the modulation transform functions at the spatial frequency of 50 lp/mm are above 0.6, and the root-mean-square radii of diffusion plaques are below 5 μm . The proposed method can determine system size and the image quality meets the requirements.