Abstract: By use of an infrared all-sky camera, the distribution and thermal information of cloud in the sky can be obtained, thus the weather conditions can be further estimated and predicted. with the equidistance projection imaging method, every point in an all -sky image can be mapped into its corresponding spatial angle via simple data processing and conversion. An easy-to-use numerical method was proposed to acquire the profile of a catadioptric mirror, which brought the property of equidistance projection and played the most important role in a catadioptric panoramic lens. With this numerical method, an f-theta catadioptric infrared panoramic sky lens operating at 8-12 m was designed for cloud observation. The sky lens had a wide field of view of 360(5~80), the calibrated distortion was less than 0.02%, and the MTF was over 0.4 at the Nyquist frequency of 14 lp/mm. The designed camera was very suitable for all-sky observation.