Abstract: A multi-band optical system was designed for the push-broom space camera covering visible，medium infrared and far infrared wavebands. The system has large aperture and low F number due to the requirement of large FOV. With the reference to various scanning and push-broom cameras at home and abroad, an optimized compact optical system was achieved by an effective beam-splitting approach, in which the aberrations of three channels were corrected respectively according to the aberration theory and system requirement. The field-of-view of the optical system is 2.93°×0.3°, and F number for the visible light is 3.8 while F number for both of medium infrared and far infrared is 1.9. The design result indicates that the optical modulation transfer functions of the three bands within the cut-off frequency are all close to the diffraction limitation.