The scheme of dual-camera combination is given to obtain high spatial resolution and wide pushbroom scanning width for airborne multispectral camera.The parameters of the optical subsystem are determined by system detecting capability estimation and user′s requirement.Subsequently,the subsystem design is pressented based on ray-tracing technique.The subsystem adopts the double-gauss configuration,which has an effective focal length of 175 mm,a field of view of 18°,an F-number of F/3.6 and the spectral range of 500~900 nm..The result is highly optimized to meet the requirement of combination.The moderate tolerance calculation results show that the system is easy to be fabricated and assembled.