Telecentric and cryogenic optical system is a good solution to space-based IR sensor with wide field, sensitivity and determination of accurate orientation. A refractive telecentric optical system was designed with squared field of view in 8 degrees, entrance pupil of 265 millimeters and operating at 200 K. The aperture of the lens was 280 millimeters. By multilevel spring holders,the opto-mechanism got a available tradeoff between enough stiffness at room temperature and stress-free at 200 K, accordingly prevents thermal stress on lens and heat leakage from room temperature supports to cryogenic lens. After lenses alignment, vibration test and image test at operating temperature were performed. The ensquared energy reached 75% on axis and 72% off-axis respectively.