Abstract: A collimator with ultra-small size, long focal length and high image quality was designed, the structure of full reflection off-axis two-mirror was used. The collimator focal length was 12 000 mm, effective aperture was 400 mm, within field of view 30 mm30 mm the wavefront aberration was better than 1/20@632.8 nm. After light turning many times , the collimator dimensions were less than 1 000 mm600 mm500 mm, the total mass was less than 60 kg. By analysis and calculation, the environmental adaptability of collimator is better, and it meets the requirement of the normal launch site test .