A kind of off-axis parabolic collimator acted as infrared target source was introduced.According to the system specific requirements.The focal length f=960mm,relative aperture 1:6,field of view 0.6°,wave length 0.8~1.4μm,the optical system was designed.Reflective optical system which can be made big aperture,light weight.Reflective optical system also do not produce chromaticaberration.Because the system can not exist center block,the off-axis parabolic system is chosen.In order to improve image quality.The system is composed of primary high order off-axis parabolic,secondary fiat mirror and compensated lens.This design of the off-axis collimator has the practical value.