In this paper, the assembly and rectification method of the new optical system is studied. According to the characteristics and difficulties of the diffraction camera, the assembly and rectification scheme is formulated. Firstly, the space angle of the mirror is determined by the spatial attitude measurement and the reference conversion matrix method. The coaxial adjustment and combined detection and adjustment of each transmission lens group are completed by the self alignment method. The method of sensitivity matrix iterative fine adjustment based on aberration is applied in the whole machine assembly and adjustment process. Finally, the high-precision assembly and detection of the complex offset axis infrared diffraction camera were completed, and the wave aberration on the axis reached 0.119λ@3.39μm. The MTF reached 0.13@33lp/mm, meeting the design requirements. This method provides engineering experience and reference for similar camera assembly and adjustment process methods. © 2023 SPIE.