The reflective optical system which is characterized by the spectrum band 450-900 nm, focal length of 5 000 mm and F number of 10 was designed.The result indicates that the field angle reaches 1.6°, optical system distortion is less than 0.5%.Modulation Transfer Function (MTF) reaches 0.65 at Nyquist frequency(25 lp/mm) with 6% central obscure, the quality of image reaches the diffraction limited.At the same time, the paper studies the static MTF of all spectrums based on using time delayed integration CCD.So this kind of optical system can meet the demand for the use of multispectral space cameras.