In this paper, the spatial positioning technology of off-Axis optical elements is studied for the installation and positioning requirements of the off-Axis mirror and the anomalous off-Axis ellipsoid mirror in an optical system. In this paper, the assembly coordinate system is established according to the global coordinate system of space optical system. The key optical parameters of the optical system are accurately measured and controlled by the theodolite, laser tracker, interferometer and other instruments, so as to realize the precise positioning of the special-shaped off-Axis optical element. Secondly, the optical characteristics of the system are analyzed by computer aided setting technology, and the optical misalignment is calculated according to the system wave aberration detection results. Thirdly, the attitude of optical element is adjusted precisely according to the amount of optical misalignment. After many iterations calculation and precision adjustment, the optical index requirements are finally achieved. The spatial positioning method of large size anomalous off-Axis optical elements proposed in this paper provides an effective method for the spatial positioning and system assembly of anomalous off-Axis optical elements in large aperture optical systems. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.