为了解决离轴三反光学系统装调过程中由于连接、紧固、温度变化等产生的应力导致反射镜面形和系统像质恶化的问题，提出了无应力结构设计和装调方法。采用内外框结合的方法设计反射镜组件，同时设置柔性变形环节，增加应力源与镜面间传递距离来削弱应力对反射镜面形的影响。系统框架采用非固定的定位方式，使用3个高精度钢球和相应的锥形孔、V型槽和平面底座约束框架的六自由度，通过两个基准立方镜和莱卡经纬仪监视框架的微位移，数显千分表监视反射镜六维调整架的移动和复位。经初装调和计算机辅助精装调后，系统全视场平均波像差均方根（RMS）值达到0.068λ；修垫、连接后为0.070λ，在奈奎斯特频率处的全视场平均调制传递函数（MTF）为0.720，均满足设计指标，得到的结果证明了装调方法的可行性。

To overcome the degradations of optical figure accuracy and image quality caused by external or internal stresses from connecting, fastening or temperature changing in the alignment process of an off-axis three-mirror system, stress-free mechanical design and system alignment methods were proposed. The impacts of the stresses on the mirrors were reduced by employing combined inner and outer mounts, setting up flexible links and increasing the delivery distance from stress source to mirror surface. The system frame was positioned without being fastened. Three high precision steel balls and corresponding a conical-hole pedestal, a V-type mount and a plate pedestal were utilized to constrain all six degrees of freedom (DOF) of the system support frame. Two Leica theodolites and two datum cubic prisms were used for monitoring the micro displacement of the support frame. Several digital micrometers were employed to monitor the movement and recovery of six-DOF adjustment mechanisms. Through preliminary and computer-aided alignments, the whole-field-of-view average Root Meant Square(RMS) wavefront error reaches to 0.068λ, and then becames 0.070λ after spacers are ground and connected to the frame. The average Modulation Transfer Function(MTF)（at Nyquist frequency）corresponding to the whole field of view is 0.720. These results meet the performance specifications and verify the feasibility of the proposed methods.