Abstract: A minitype optical system used in stereo camera was designed based on civilian low cost stereo imaging requirement, the optical system aimed to achieve 50 m ground sampling distance at 250 km orbit altitude. This optical system can both achieve stereo imaging function and large format array imaging function combined with a CMOS. The system has a focal length of 32 mm, a field of view of 66, an F-number of 6.8 and a working wavelength range of 450-750 nm. The optical system consists of two parts of optical configurations-retrofocus lens and apochromatic microscope. The system design value of MTF achieves 0.49@78 lp/mm, distortion value less than 0.1%, the relative illumination of marginal field of view achieves 0.83, principal ray incoming angle in image plane of marginal field less than 15. The testing result after optical mounting centering alignment shows that the MTF of each field of view all achieve 0.4@80 lp/mm,which meets the static MTF requirement in laboratory. This optical system has better performances in imaging width and distortion value compared with other international famous stereo cameras.