With the rapid development of large field of view, large aperture and unobstructed space optical imaging system, the optical imaging system structure has developed from aspherical coaxial and off-Axis free surface off-Axis. Free surface is applied to multi reflective Off-Axis optical system to balance the sharply increased off-Axis aberration. Because the free-form surface does not have symmetry, the full free-form surface multi reflective Off-Axis optical system has lost the rotational symmetry of the traditional optical system in structure, resulting in more degrees of freedom in the installation and adjustment of the full free-form surface multi reflective Off-Axis optical system, the relationship between optical axes of various optical elements is complex, the system integration is more difficult, and the installation and adjustment process is difficult to monitor. Based on this, the paper proposes a precise alignment process method of the full free-form surface multi reflection Off-Axis optical system. The space global coordinate system is established through the space coordinate measurement equipment, and the precise attitude of each reflector is monitored by combining the self-Aligning Theodolite and cube mirror, and the reference transfer space position is measured by using the self-Aligning microscope and the measurement target ball. he engineering project verification shows that this assembly and adjustment process method realizes the unification of the design, processing and assembly and adjustment benchmark of the full free-form surface multi reflection Off-Axis optical system, has strong operability, reduces the difficulty of assembly and integration, and the comprehensive measurement accuracy is better than 0.01 mm. The wave aberration RMS of the final refrigeration relay long wave infrared camera system is better than 0.45 λ @ 632.8nm, meeting the design specifications. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.