Optical system of a space fisheye camera based on 1/3 inch (1 inch=25.4 mm) CCD is designed considering the space environment. The focal length of the fisheye optical system is 2.1 mm, the F number is 4, and the field of view is 210°. The required working temperature is between -40 ℃-+60 ℃. After careful studying the influence of space environment such as the space γ radiation and ultraviolet radiation, temperature change and vacuum on the optical system, the technique for keeping image quality in space environment is put forward. The fisheye lens can reach excellent imaging quality in such an austere environment, and provide important guarantee for information capture with extreme wide-angle view on the orbit.