With the development of space optical technology,space camera is required to be characterized by both high resolution of ground sample distance and ability of multi-spectral imaging.Thus the optical system design must be satisfied with the demand of large field of view and small distortion.Based on the on-axis three-mirror-anastigmat system,a new type of optical system was designed,which is characterized by small central obscuration,low optical distortion and reasonable arrangement of panchromatic and multi-spectral CCD.The results indicate that the field angel reaches 1.6°,the system line central obscure coefficient is lower 1/3,the optical system distortion is less than 0.5%,MTF is superior to 0.47 at 50 lp/mm,the image quality reaches the limit of optical diffraction,when the focal length is 12 000 mm,focal ratio is 12, and the spectrum band is from 450 to 900 nm.So the proposed optical system can meet the demand of high resolution multi-spectral space cameras.