Abstract: During the designing process for large diameter catadioptric infrared, the aberrations of primary and secondary mirrors are calibrated separately, which makes the precise alignment difficult. For this problem,an assistant alignment lens used for infrared optical system was designed, which could compensate the aberrations to accomplish system alignment with high-precision. The manufacture precision of assistant alignment lens was exactly controlled to reduce error caused by itself in manufacturing process.The designed wave aberration data of system is 0.14 and the practical data is 0.3 after operated using ZYGO interferometer. At last, the secondary imaging lens was used in stead of assistant alignment lens.The result shows that the image quality of the optical system can satisfy the demand of infrared search and tracking system.